///J 
 
 *a 
 
 "b^ 
 
 
 ^> 
 
 IMAGE EVALUATION 
 TEST TARGET (MT-3) 
 
 /. 
 
 V ^ ^ Zip 
 
 1.0 
 
 I.I 
 
 — 6" 
 
 •^ 1^ 12.2 
 
 It lifi lllllio 
 
 1.8 
 
 11-25 11.4 IIIIII.6 
 
 
 /: 
 
 % 
 
 ^$ ■.>* 
 
 :^' 
 
 ^y 
 
 *v# 
 
 '/ 
 
 ///. 
 
 Photographic 
 
 Sciences 
 
 Corporation 
 
 33 WEST MAIN STREET 
 
 WEBSTER, NY. 14580 
 
 (716) 872-4503 
 

 CIHM/ICMH 
 
 Microfiche 
 
 Series. 
 
 CIHM/ICIVIH 
 Collection de 
 microfiches. 
 
 Canadian Institute for Historical Microreproductions / Institut canadien de microreproductions historiques 
 
 :<> 
 
Technical and Bibliographic Notes/Notes techniques et bibliographiques 
 
 The Institute has attempted to obtain thid best 
 original copy available for filming. Features of this 
 copy which may be bibliographically unique, 
 which may alter any of the images in the 
 reproduction, or which may significantly change 
 the usual method of filming, are checked below. 
 
 L'Institut a microfilmi le meilleur exemplaire 
 qu'il lui a M possible de se procurer. Les details 
 de cet exemplaire qui sent peut-dtre uniques du 
 point de vue bibliographique, qui peuvent modifier 
 une image reproduite, ou qui peuvent exiger une 
 modification dans la m6thode normale de filmage 
 sont indiquAs ci-dessous. 
 
 Coloured covers/ 
 Couverture de couleur 
 
 — — 
 
 Coloured pages/ 
 Pages de couleur 
 
 Covers damaged/ 
 Couverture endommag^e 
 
 
 Pages damaged/ 
 Pages endommagdes 
 
 Covers restored and/or laminated/ 
 Couverture restaurde et/ou pellicul^e 
 
 
 Pages restored and/or laminated/ 
 Pages restauries et/ou pellicul^es 
 
 Cover title missing/ 
 --. Le titre de couverture manque 
 
 y 
 
 Pages discoloured, stained or foxed/ 
 Pages ddcolor^es, tachetdes ou piqu6es 
 
 Coloured maps/ 
 
 Cartes gdographiques en couleur 
 
 
 Pages detached/ 
 Pages ddtach^es 
 
 Coloured ink (i.e. other than blue or black)/ 
 Encre de couleur (i.e. autre que bleue ou noire) 
 
 V 
 
 Showthrough/ 
 Transparence 
 
 1 1 Coloured plates and/or illustrations/ 
 Planches et/ou illustrations en couleur 
 
 
 Quality of print varies/ 
 Qualit6 indgale de I'impression 
 
 Bound with other material/ 
 Relid avec d'autres documents 
 
 
 Includes supplementary material/ 
 Comprend du materiel supplementaire 
 
 Tight binding may cause shadows or distortion 
 along interior margin/ 
 
 
 Only edition available/ 
 Seule Edition disponible 
 
 D 
 
 D 
 
 Lareiiure serr6e peut causer de I'ombre ou de la 
 distortion le long de la marge intirieure 
 
 Blank leaves added during restoration may 
 appear within the text. Whenever possible, these 
 have been omitted from filming/ 
 II se peut que certaines pages blanches ajouties 
 lors d'une restauration apparaissent dans le texte, 
 mais, lorsque cela itait possible, ces pages n'ont 
 pas ix6 filmdes. 
 
 Additional comments:/ 
 Commentaires suppldmentaires; 
 
 n 
 
 Pages wholly or partially obscured by errata 
 slips, tissues, etc., have been refilmed to 
 ensure the best possible image/ 
 Les pages totalement ou partiellement 
 obscurcies par un feuillet d'errata, une pelure, 
 etc., ont 6t^ filmdes d nouveau de facon d 
 obtenir la meilleure image possible. 
 
 Tl 
 to 
 
 Tt 
 
 P< 
 of 
 fil 
 
 Oi 
 be 
 th 
 sii 
 ot 
 fir 
 sit 
 or 
 
 Th 
 sh 
 Tl 
 w 
 
 Mi 
 di 
 
 enl 
 be 
 rig 
 rei 
 mi 
 
 This item is filmed at the reduction ratio checked below/ 
 
 Ce document est film6 au taux de reduction indiqui ci-dessous. 
 
 10X 14X 18X 22X 
 
 26X 
 
 XX 
 
 v/ 
 
 12X 
 
 16X 
 
 20X 
 
 24X 
 
 28X 
 
 32X 
 
The copy filmed here hee been reproduced thanks 
 to the generosity of: 
 
 Library, 
 
 Gsological Survey of Canada 
 
 L'exemplaire filmA fut reproduit grflce A la 
 g4nArosit6 de: 
 
 Bibliothique, 
 
 Commission Gtologique du Canada 
 
 The images appearing here are the best quality 
 possible considering the condition and legibility 
 of the original copy and in keeping with the 
 filming contract specificetions. 
 
 Original copies in printed paper covers are filmed 
 beginning with the front cover and ending on 
 the last page with a printed or iilustreted impres- 
 sion, or the back cover when appropriate. All 
 other original copies are filmed beginning on the 
 first page with a printed or illustrated impres- 
 sion, and ending on the last page with a printed 
 or iliuittrated impression. 
 
 The last recorded frame on each microfiche 
 shall contain the symbol -^ (meaning "CON- 
 TINUED"), or the symbol V (meaning "END"), 
 whichever applies. 
 
 Les images suivantes ont 6t6 reproduites avec ie 
 plus grand soin, compte tenu de la condition et 
 de la nettetd de l'exemplaire f ilmi. et en 
 conformity avec les conditions du contrat de 
 filmage. 
 
 Les exempiaires originaux dont la couverture en 
 papier est imprimie sont fiimAs en commenpant 
 par Ie premier plat et en terminant soit par la 
 derniAre page qui comporte une empreinte 
 d'impression ou d'illustration, soit par Ie second 
 plat, selon Ie cas. Tous les autres exempiaires 
 originaux sont film^s en commen9ant par la 
 premidre page qui comporte une empreinte 
 d'impression ou d'illustration et en terminant par 
 la derniire page qui comporte une telle 
 empreinte. 
 
 Un des symboies suivants apparaitra sur la 
 dernidre image de cheque microfiche, selon Ie 
 cas: Ie symbols — ► signifie "A SUIVRE ", Ie 
 symbolb y signifie "FIN". 
 
 Maps, plates, charts, etc., may be filmed at 
 different reduction ratios. Those too large to be 
 entirely included in one exposure are filmed 
 beginning in the upper left hand corner, left to 
 right and top to bottom, as many frames as 
 required. The following diagrams illustrate the 
 method: 
 
 Les cartes, planches, tableaux, etc., peuvent dtre 
 fiimds d des taux de reduction diffdrents. 
 Lorsque Ie document est trop grand pour dtre 
 reproduit en un seul cliche, il est film6 d partir 
 de I'angle sup6rieur gauche, de gauche d droite, 
 et de haut en bas, en prenant Ie nombre 
 d'images ndcessaire. Les diagrammes suivants 
 illustrent la mdthode. 
 
 1 
 
 2 
 
 3 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
ON THE 
 
 ORieiN Of ERUPTIVE AND PRIMARY ROCKS, 
 
 BY THOMAS MACFARLANE. 
 
 (Prexented to the Natural History Society.) 
 
 On a former occasion, * I had the honor of presenting to this 
 Society a series of papers describing the primitive fornaations 
 as they occur in Norway, and comparing them with their Cana- 
 dian equivalents. I then confined myself to a simple statement 
 of the facts known regarding these formations, referring to their 
 constituent rocks, to their structure, and to the order of their 
 succession, but abstaining altogether from any attempt to pro- 
 pound a theory which might explain the various phenomena 
 described. I subsequently! however gave a translation of a 
 chapter from Naumann's classical Lehrhuch der Geognosie, wherein 
 the various views entertained by geologists as to the origin of 
 these formations, are plainly and impartially stated. It there 
 appears, that although there exists an extraordinary diversity of 
 opinion among geologists on this subject, there are two distinct 
 and opposing theories, under one or other of which those different 
 views may be classified. Tho first of these theories, and the one 
 adopted by the majority of geologists, supposes the primitive or 
 primary rocks to have resulted from the alteration or metamor- 
 phism of sedimentary strata. The second theory supposes them, 
 in part at least, to represent tlie first solidified crust of our 
 planet. 
 
 Although these opposing theories might with justice be 
 respectively termed, so far as they refer to the origin of the 
 primary rocks, the aqueous or metamorphic theory, and the 
 igneous theory, still they must not be considered as bearing the 
 slightest relation to the old theories adopted, and so pertinaciously 
 
 » Canadian Naturalist, Vol. VII, p. 1. 
 t Canadian Naturalist, Vol. VII, p. 254. 
 
OllKlIN OF ERUPTIVE AND PBIMARV RO(!KS. 
 
 argued by the neptunists ar.d plntonisls. The question in dispute 
 then, referred to the origin of the undoubtedly intrusive and 
 unstratified rocks, — granite, porphyry, basalt, &c. So far however 
 as concerns the primitive stratified rocks, Werner and Hutton 
 both regarded them as of sedimentary origin, although they 
 diflered as to the state in which they were deposited ; and Hutton 
 alone considered it necessary to explain their crystalline con- 
 dition by the metamorphic action of heat. Indeed, instead of 
 there being any analogy between the old controversy and the 
 })rosent question, it happens that Hutton, the founder of the 
 plutonic school of former dayii, v/aspflie originator of the theory 
 at present prevailing of the aqueous origin of the primary 
 stratified rocks. 
 
 On the other hand, it is scarcely possible to say who was the 
 author of the igneous theory, although the writings in which 
 it was propounded are of comparatively recent date. Probably 
 among its earliest supporters was Sir H. T. De la Beche, who 
 thus expresses himself on the subject: — "If we consider our 
 " planet as a cooling mass of matter, the present condition of 
 " its surface being chiefly due to such a loss of its original heat 
 " by long continued radiation into the surrounding space, that 
 *' from having been wholly gaseous, then fluid and gaseous, and 
 " subsequently solid, fluid and gaseous, the surface at last became 
 " so reduced in temperature, and so little affected by the romain- 
 " ing internal heat, as to have its temperature chiefly regulated 
 " by the sun, there must have been a time when solid rock was 
 " first formed, and also a time when heated fluids rested upon it. 
 " The latter would be conditions highly favorable to the pro- 
 *' duction of crystalline substances, and the slate of the earth's 
 '' surface would then be so totally different from that which now 
 " exists, that mineral matter even abraded from any part of the 
 " earth's crust which may have been solid, would be placed under 
 " very diff"erent conditions at different periods. We could scarcely 
 " expect that there Avould not be a mass of crystalline rocks 
 " produced at first, which, however they may vary in minor 
 " points, should still preserve a general character and aspect, the 
 " result of the first changes of fluid into solid matter, crystalline 
 " and sub-crystalline substances prevailing, intermingled with 
 " detrital portions of the same substances, abraded by the move- 
 " mcnts of the heated and first formed aqueous fluids." * 
 
 a • • • 
 
 ^ d • ■ ■ ■ 
 
 *• IftpOft ou the Geology of Cornwall, Ac, p. 32. 
 
 • •• 
 
 • * • 
 
 • • • • 
 
 I • • • 
 
 
 .••• 
 
 • • • • 
 
 ' ; • • • : ' 
 
 
 • • •< 
 
 • • • •. 
 
ORiaiN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 8 
 
 
 rs 
 
 le pro- 
 earth's 
 
 it 
 
 t 
 
 < 
 
 ch now 
 
 -■■ 
 
 of the 
 
 
 i under 
 
 
 carcely 
 
 
 i rocks 
 
 
 minor 
 
 ; 
 
 jct, the 
 
 ■; 
 
 italline 
 
 ,■ 
 
 with 
 
 i 
 f 
 
 move- 
 
 
 
 ,! 
 
 
 V 
 i 
 
 1 
 
 
 i 
 
 Although this language is somewhat indefinite, still the idea 
 embodied in the igneous theory is shadowed forth in it, and on 
 the whole this quotation may be considered as the text of the 
 present essay. It is I believe possible to maintain, with every 
 appearance of reason, that the Primitive Gneiss formation con- 
 stitutes the first solidified crust of the originally fused globe, 
 and that the crystalline and sub-crystalline rocks of the Primitive 
 Slate formation are the products of a peculiar transition period, 
 during which aqueous fluids gradually accumulated on the surface, 
 and the latter attained a temperatures approachingf somewhat to 
 that of the present day. 
 
 In attempting to show that this proposition is supported by 
 geological evidence, I shall confine myself principally to arranging 
 and elaborating the facts and arguments in support of it, which 
 T have found scattered through a considerable number of geo- 
 logical papers and manuals. I shall also, in order to state the 
 case with full force, be obliged to insert prefatorily much of what 
 may be considered as mere elementary facts in physical geography 
 and geology. I shall first refer to the evidences which we 
 possess regarding the internal heat of our planet and its density, 
 deducing from them certain concliisions as to the present con- 
 dition of the interior of the earth, ^n doinfj so, I shall allude 
 to the nature of certain volcanic products ; and then continuing 
 the considerations of the constitution and mode of occurrence 
 of igneous rocks, I shall search back through the \arious eruptive 
 formations for evidences of the nature of the igneous action 
 which has taken place in former periods of the earth's history, 
 and ultimately arrive at the consideration of the theory of the 
 earth's original state of igneous fluidity. This theory, univer- 
 sally admitted by geologists, will then afl'ord us a firm starting 
 point for some speculations as to the process of the first solid- 
 ification of the earth's crus(, and the origin of gncissoid rocks. 
 Pursuing the subject further, T shall endeavour to shew that 
 the peculiar rocks of the Primitive Slate formation are also pro- 
 ducts of the action of the first condensed fluids on the heated 
 crust of the earth. There are few theories whereon such a 
 unanimity of opinion exists among geologists, as that of the 
 originally fused condition of our planet, and few formations 
 regarding the origin of which more uncertainty prevails than 
 that of the primitive formations. If therefore it can be shewn 
 to be probabh* that those ])riiiiitive forniations have merely 
 
ORiaiN op ERUPTIVE AND PRIMARY ROCKS. 
 
 resulted from an originally fused globe in the process of cooling, 
 much will have been done toward filling up a great gap in the 
 history of the earth's development. 
 
 I. The Temperature and Density of the Interior of our 
 Planet. 
 
 It will no doubt seem to manv that the matters to be treated 
 of in this chapter, are far beyond the limits of the subject of 
 the present paper. Since, however, the originally fused condition 
 of our planet, and the constitution of its mass, are at the founda- 
 tion of the igneous view of the origin of the primitive gneiss 
 formation, it would seem necessary to refer to the reasonings upon 
 which the idea of a fused globe, and the various theories pro- 
 pounded regarding the structure of the interior of our planet, 
 are based. Many of these reasonings are founded on phenomena 
 observable at the present day, which point to the existence of 
 intense heat and extraordinary density in the centre of the earth. 
 Hence this proposed recapitulation of the evidences of internal 
 heat and density may not be out of place. 
 
 Whatever may have been the temperature of the earth's 
 surface in the former periods, it is abundantly evident that it is 
 now altogether regulated by the sun. Since the influence of 
 the sun's rays penetrates to some extent beneath the surface, and 
 aifects the degree of temperature there existing, it will be neces- 
 sary to define the extent to which this takes place, before pro- 
 ceeding to advert to the influence of the subterranean heat on 
 the temperature of the earth's crust. It is obvious that the 
 influence of the sun's rays is exerted very irregularly, and that 
 variations in the degree to which the surface of the earth is 
 affected by it occur throughout the day, and annually. The 
 diurnal variations are of course not so great as those of the year, 
 and the latter vary of course with the situation of the point of 
 observation. These diurnal and annual variations are less and 
 less felt, the deeper, to a certain point, we penetrate beneath the 
 surface. Towards this point the extremas of temperature grad- 
 ually approach nearer to each other, the differences are gradually 
 equalized, and finally | they disappear completely. The depth 
 at which this point of constant temperature exists varies with 
 latitude and climate, and with the capacity for conducting heat 
 which the surface possesses. In African deserts, where the sand 
 has been found to possess sometimes a temperature of 40° to 48° 
 
ORIGIN OP ERTTPTTVE ANT) PRIMARY ROnKP. 
 
 n 
 
 li, * the point of constant temporiiture is near the surface, becaine 
 the annual variations are comparatively small. The avorago 
 temperature of the warmest month in Singapore is 22.40 * K., o^ 
 the coldest month 20.(i ^ R. f The yearly variation therefore, 
 does not exceed 1.8'^ R., and consequently the point where the 
 extremes equalize themselves must he very near the surface. In 
 higher latitudes however, where the variations are greater, (London 
 11.80 « R., Paris 13.50® R., New York21.'70® R.,) the point 
 of invariable temperature lies deeper. In the temperate zone, the 
 daily variations disappear at adepfch of from three to tlve feet, and 
 the annual variations at a depth of from 00 to 80 feet beneath 
 the surface. The celebrated thermometer placed 80 feet beneath 
 the surface in the vault of the national observatory at Paris in 
 1783, shews constantly a temperature of 9.60° R.| Since the 
 average temperature of Paris is 8.60 '^ R., it would therefore appear 
 that even at this depth of 80 feet the influence of the central 
 heat begins to make itself felt. 
 
 As early as the year 1678, the Jesuit Athanasius Kircher was 
 informed by Hungarian miners that a higher temperature existed 
 in the depths of mines, than on the surface of the earth, and 
 Von Trebra, in l78r), mentions the same fact.§ Not only was 
 practical experience of the existence of a subterranean source of 
 heat tirst obtained by miners, but the first experiments made 
 with the view of ascertaining the temperature of the earth's 
 crust at greater depth, were instituted in mines. The results of 
 these experiments constituted for a long time the only proofs of 
 the increase of the temperature with the depth. It cannot be 
 denied however that the observations made in the shafts and 
 underground working of mines are subject to various disturbing 
 influences, so that it would appear that at least the earliest 
 of these observations are less to be relied upon than those from 
 other sources. But sitice they shew a general coincidence they 
 furnish, when taken in connection with other observations, a com- 
 plete confirmation of the fact of the increase of temperature with 
 the depth. The results of the experiments instituted '.n mines, 
 differ in value according as they have reference to the tempera- 
 
 * Poiiillet ; MuUer, Lehrbucb der Physik aud Meteorologie, Vol 11^ 
 p. 724. 
 
 t Ibid 11, 710. 
 
 t Queustedt, Rpochen der Natur, p. 13. 
 
 c Ibid p. IJ, 
 
6 ORIUIN OP RRIIPTIVE ANT) PTHMARY ROOKS. 
 
 ture of the air, watoi or rock there occuiriug. Thoso obtained From 
 observations made on the rock plainly <ieHorve njost confidence.* 
 Not only in European niinc»,butin thosiiof South America, Mexico, 
 the United States, and the East Indies, observations have proved 
 that the temperature inereases with the depth, and shewn that it 
 remains invariable at one and the same depth, jtrovidod no disturb- 
 ing causes are at work. In I1i40, (rensanne instituted experiments 
 at Giromagny in the Vosges which gave the following results : — 
 At a depth of 
 
 339 feet tlie teiuperiiturL' was 12. !> ® . Centigrade. 
 
 634 " " " 13.1* " 
 
 048 " " " 19.0® " 
 
 1333 " " 22.7° " 
 
 Saussure obtained the following results at Hex in the Canton 
 Waadt, in a shaft in which no one had been for three months 
 previously. 
 
 Depth. Temperature. 
 
 322 14,4 o Centigrade. 
 
 564 15.0° " 
 
 677 17.4° " 
 
 Similar observations wore afterwards made in the mines of 
 Freiberg by d'Aubuisson, Von Humboldt, and Von Trebra ; in 
 the mines of Cornwall by Forbes, Fo.x, and Barkam, and in tlie 
 Anzasca valley by Fontanetti. The most comprehensive and 
 exact observations were however those made at the instance o 
 the government mining officials of Saxony and Prussia, in the 
 mines of those countries. The observations in the Prussian mines 
 led to the following resulta.f 
 
 1. That a decided increase of temperature take.^ places with 
 
 increase of depth. 
 
 2. That the temperature at every greater depth is invariable, 
 
 since the annual oscillations were at the most only 1 ^ . 
 3- That the depth corresponding to an increase of temperature 
 
 of 1 "^ , differs extremely in different localities, varies from 
 
 48 to 365 feet, and on an average amounts to 167 feet. 
 4. That the temperature increases twice as rapidly in coal mines 
 
 as in ore mines. 
 
 * Naumann, Lehrbuch der Geognosie, I, 49. 
 t Poggend. Ann ; vol. xxii, 1831, p. 497. 
 
* 
 
 t 
 
 OFiroiN OF ERtipTlVR AND f'KIMARV BOrRfJ. 7 
 
 5. I'liat tho oWrvations <li<l nol HlVonldaU Hutruicnlly decided 
 for tho establishment of any law as to tho progrnssion of 
 tho increase nf teraporfiturc. 
 
 Tho exporimonts instituted in the Saxony mines wiire under th 
 careful direction of lleicli, and made wflU very good thormorne- 
 ters, sunk forty inchos into the solid rock, and with every possible 
 precaution. They yielded tho following results.* 
 
 1. That the teniperaturo increases decidedly with tho depth. 
 '2. That tho teniperaturo is invariable at every ono point of 
 observation. 
 
 3. That the average distance, (corresponding to an increase nf 
 
 one degree Reaumur in temperature, is 129 foet. 
 
 4. That a general law with regard to the relative increase of 
 
 temperature cannot be deduced from these experiments. 
 
 5. That the rock in the underground workings and in the course 
 
 of time becomes somewhat cooled by tho air of tho mine, 
 and that on the whole the cooling influences overbalance 
 the heating ones. 
 
 Among other observations the following may be mentioned : — 
 The distance corresponding to an increase of temperature of one 
 degree was detorminod by : 
 
 Oldham in ^Vaterford, Ireland, as 165 Peel. 
 
 Phillips in New Castle 100 " 
 
 Hodgkiuson in Manchester 115 " 
 
 Hiuzeau in Belgium 102 " 
 
 Cordier near Canneaux ™ ........ 1 ] 1 "f 
 
 It will be observed that in th(i observations mentioned above, 
 the depth corresponding to an increase of 1 "^ varies from 92.',i 
 to 161 feet. 
 
 Conclusive as are tho experiments in mines with regard to 
 the increase of temperature, they after all refer only to compara- 
 tively slight depths. The depths at which observations have been 
 made in artesian wells exceed those of the mine experiments. As 
 is well known, by means of tliese artesian wells, a vent is opened 
 ■whereby the water of subterranean reservoirs or springs, confined 
 
 • Reich : Beohachtungen iiber die Temperatur dcs Gesteines, 1834. 
 t Naumann ; Lehrbuch der Geognosie, I, 54. 
 
I 
 
 8 ORIGIN OF KRIU'TIVK \NT) I'RIMAUV ROfRS. 
 
 Rt frycui fIcptliK, firulH a pfisHugti to the surffico. This water, liaving 
 I'utind iU way from tho Hurfuoo into tlioxc doplliH, in general ly 
 Hiibject to a vory strong hydnrntatic prnssiiro, and [(OssesHcs tho 
 t»Mnporatiirc of tlm depth from which it is hborated. The 
 bnro-holcs, bv moans of which tliesM sulitcrrranoan rt'sorvoirs arc 
 tap|>e<l, aru (ispticially tittcd for cxpcrimutit> hm to tho toDi[)ura- 
 turos of various d(^ptli!s, since tlieir (h^pth, while being borod 
 is accurately known, and sinco thoy aro alwaya filled with water. 
 Huch cxporimcnts havo ropoatodly been made, and have led to th(! 
 complete and incontrovertible confirmation of tho fact that the 
 temperature of every constant depth, beneath tho influences of 
 tlio variations of tomporaturo on the surface is invariable, and 
 that flu; temperature increases continuatly with the depth. The 
 following tables contain some of the most remarkable obscrva- 
 tions of tliis nature. 
 Artesian well at lludersdorf, near IJeriin : — 
 
 Dopth. Tcmperatun', 
 
 380 feot 17.12° Ccntigrftde. 
 
 500 " IT-TO" •• 
 
 655 " 19.75" '< 
 
 880 " -.23.50" <« 
 
 Artesian well of < Jrenelle, in Paris : — 
 
 Depth. Temperature. 
 
 'J17 feet 22.aO° Ooniigradc , 
 
 1231 " 23.75" <* 
 
 1555 " 20.43'* " 
 
 1G84 >' 37.70" '• 
 
 Artesian well of Neusakwerk, Westphalia : — 
 
 Depth. Temperature. 
 
 580 feot 19.7 « Centigrade. 
 
 1285 " 27.5° «« 
 
 1935 " 31.4'= '« 
 
 2144 " 33.0 » " 
 
 In tho artesian well at Moudorfl', in the (Irand Duchy of 
 Luxemburg, at a depth of 200G feet, a temperature of 34 ® Cen- 
 lii^rade was oven observed. We have already seen that the results 
 of the experiuKiTits in mines, as to the depih corresponding to one 
 degree of increase, varied considerably. Tho results obtained in 
 artesian wells as to this point were much more satisfactory. The 
 distance corresponding to an increase of 1 ® was found to be: 
 
 I 
 
ORIGIN OF ERUPtlVI AJTb PRIMART ROOKS. 9^ 
 
 At Rouen 00. 8 Feet. 
 
 AtMondorflT 01. 1 «* 
 
 At ItUiiiTsdorf 02. '< 
 
 At Ncutiiilxwerk 03.27 " 
 
 At(}rinellc 05. " 
 
 AiSt. Anaro(Rure) OS. 3 '' 
 
 Thene rosulU ^iliow a reirmrkicble coincidence, bnt tliore Are 
 otliorH wliicli shew uxtraordinary ditforoticos, sucli as tho t'uUow- 
 ing:— 
 
 At La Rochelle 60. G Foet. 
 
 At I'itzbuhl near Magdebarg 80. " 
 
 At Artuui ia ThUringia, 120'. "• 
 
 Tlieno latter results, as well as those ditforing widely from enoh 
 other, which have Insen obtainofl in mines, are not to be regarded 
 aa at all invalidating tho general result. These diftorences may 
 be cauHed by variations in the conducting capacity of the various 
 rocks; by the neighborhood of subterranoan watercourses; but 
 especially by the greater or lesser distance of the point of obser- 
 vation from the «ource of the internal heat ; in other words by the 
 varying thickness of the earth's crust. 
 
 We have thus seen that actual observations have been made 
 aa to the tompurature of the crust at varions depths beneath the 
 surfftce, sotuetiines as much aa 2000 feet, and the result of these 
 has been to prove that an increase of temperature takes |ilacO' 
 with the deiith, amountir>g on the average to about 1 ° Cent, for 
 every 100 feet. We have ne.\t to enquire as to whether any increase 
 of temperature takes place at still greater depths. Wo have 
 abundant proofs that this further increase does take \>\hcc, in thtf 
 tomperatnres of the thermal springs so widely distributed over ' 
 every part of the surface of the globe. Those temperatures are^' 
 much hi<;her than those which have been observed in mines or 
 artesian wells. The waters of these springs rush with extraordi^' 
 nary force out of the ground, from which circumstance wo may con- 
 clude that they ascend from their sources, with a rapidity which 
 does not permit them to cool very considerably in their passage* 
 through the upper and colder strata. Although we are ignorant' 
 of the exact depth from which the waters of these springs 
 rise, we are nevertheless justified in assuming that they come' 
 from greater depths than those of mines or artesian wells. 
 
 * Naumana'i Geoga(Mrt«|' I^ 46. 
 
 B 
 
I 
 
 10 ORIGIN OP ERUPTIVB AND PRIMARY ROCKS. 
 
 The highest temperature yet observed in the latter was at 
 MundorfF, viz,, 34 ® Centigrade. The following is a list of re- 
 markable thermal springs whose temperatures: exceed that just 
 mentioned. 
 
 * n 
 
 Spring. Temperature, 
 
 Pfaffers 37.2 o Centigrade.' 
 
 Wildbad 37.5 « " 
 
 Barreges. 40.0 o " 
 
 Aix-la-Chapelle 44® to57.5«> " 
 
 Bath 46.25 o " 
 
 Leuck 50.2 «> " 
 
 Aix in Savoy 64.3 o " 
 
 Ems 56.25. « " 
 
 Baden-Baden 67.5 « « 
 
 Wiesbaden *. 70.0 » " 
 
 Carlsbad.. 75.0* " 
 
 Burtscbeid , 77.5 ^ " 
 
 Eatberine Spring in Caucasia 88.7'^ *' 
 
 Trincheros in Venezuela 97.0 °* " 
 
 We have here a series of temperatures, from the warmest yet 
 observed in artesian wells to that of boiling water, and it would 
 seem not unreasonable to suppose that the ditferences in their 
 temperatures correspond to differences in the depths of their 
 sources. It is true that the neighborhood of volcanoes or of 
 igneous rocks may heighten the temperature of springs rising from 
 comparatively shallow depths, but it is also the case that many 
 very hot springs occur in districts far distant from volcanic 
 regions. Thus it is with the hot spring of Hammam-mes-Kutin, 
 betwixt Bone and Constantine, the temperature of which is 
 stated at from 60 ® to 95 ® Cent. ; and also with the warm 
 springs in Cape Colony, which, according to Kraus, break forth 
 from sandstone, far from any plutonic rock.f It is clearly impos* 
 sible to account for the diflferences in the temperatures 
 of thermal springs in any other way than by supposing 
 that the springs possess very nearly the temparatures of the 
 depths from which they rise, and that the higher the temperature 
 o^ the water the deeper is the source from which it springs. We 
 are therefore justified in regarding it as fully proved that the tem- 
 erature of the earth increases with the depth, until a point is 
 
 * Mailer's Kosmxsche Pbyiik, p. 340. 
 t Kaumaan's Geogaosjie, I, 306. 
 
ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 
 
 11 
 
 reached at w))ich water boils. It is a matter of much difficulty 
 however to determine, with any degree of precision, the depth at 
 which this heat is attained. If we assume that the same increase 
 of 1 ® Centigrade for every 100 fe^t depth, which takes place at 
 the surface, continues to greater depths, the calculation is very 
 simple. The temperature of the Mondorflf artesian well was 34 ® 
 Cent, at a depth of 2066 feet. If we add 100 feet for each 
 of the remaining 66 ® C, we have a temperature of lOO ® C, at 
 a depth of 8666 feet. It will however be shewn in a subsequent 
 part of this paper, that we are not justified in assuming that the 
 increase of temperature follows such a regular progression, that 
 the rapidity with which the temperature increases, diminishes with 
 the depth, and that consequently the depth at which a constant 
 temperature of 100" C. reigns, is much more considerable than that 
 above stated ; that it is at least 10,000 feet, and probably even as 
 much as 20,000 feet.* It is quite possible thi t, under the great 
 pressure which must exist at this latter depth the boiling point 
 of water may be higl'er than 100 ® C, but then however, this 
 might be it could not retain this higher temperature until it 
 reached the surface. Because however rapidly it might ascend, 
 its temperature would on the way decrease with the removal of 
 the pressure, steam being at the same time generated. It is not 
 improbable that the waters of the Geyser and the Strokkr have 
 at their sources a much higher temperature than 100 ® C, and 
 that the eruptions observable at these springs are caused by the 
 generation of steam in the canal of egress, owing to the removal 
 of the pressure. This view is supported by the observations made 
 on the temperature of these springs. The water of the Geyser at 
 the surface has a temperature of 76 ® to 89 ® G., but at a depth 
 of twenty-two meters it is from 122 ° to 127 ® C. The water of 
 the Strokkr is contiimally boiling at the surface, and has, at a depth 
 of forty-one feet, a temperature of 114 ® C.f But although it is 
 possible for water to exist at a much higher heat than 100 ® C, 
 at such great depths, it is nevertheless also evident that at still 
 greater depths, and increased temperatures, it can only exist in 
 the form of steam. We can moreover readily conceive a depth 
 and temperature to which it would be impossible for water to 
 penetrate. If the temperature of the earth's crust continues to 
 
 * Naumann, Geognosie, I, 66. 
 
 t Krug TOQ Nidda, in Karsten's Archie fur Mineralogie, &c., iz, 247. 
 
smma 
 
 la 
 
 ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 
 
 increase with the depth, there rauat exist at some depth, sufficient- 
 ly great, a point beyond which the rocks are heated to suuh an 
 extent that before water can penetrate to them it ia resolved into 
 steam and expelled. 
 
 Beyond this point there ia a long interval, regarding; the in- 
 crease of temperature in which, we have no direct evidence until 
 we arrive at that furnished by tiie fused rock which in the form 
 of lava is poured forth by volcanoes, which are even more widely 
 and generally diatribated over the earth's surface than thermal 
 springs. This however supplies indirect evidence sufficient to 
 prove that daring thia great interval the heat must in- 
 crease with the depth, until the temperature of fused lava 
 is reached, at which point we must suppose eveiy thing to 
 be in a fluid state, and consequently the temperature 
 from that point to much greater depths to continue about the 
 same. The lavas which have been emitted by volcanoes in historic 
 times, have been both of a tracliytic and a basaltic nature, but 
 those of the latter character seem to have predominated. Many 
 of these doleritic or augitic lavas from very recent lava-streams 
 have been described and analysed. They are of a comparatively 
 basic composition, seldom contain more than 50 per cent of silica, 
 and are much richer than other volcanic rocka in iron-oxide. 
 The lava which constituted the stream from Etna, that de^royed 
 a great part of Cataaia in 1669, had the following composition :— 
 
 Silica 48.83 
 
 Alumina 16.15 
 
 Protoxide of iron 16. 32 
 
 Protoxide of manganese 54 
 
 Lime 9.31 „, „„ 
 
 If • A ,,0 f 34.97 
 
 Magnesia 4.58 
 
 Soda with some potash 3.45 
 
 Potuah 77 
 
 99. 95.* 
 
 This analysis bears a genera) resemblance to those of other' 
 angitic lavas. It also bears a resemblance to that of the slag 
 produced in smelting the copper schists of Mansfeldt. According 
 to Huffman, the composition of the slag produced at Kupfoi; 
 Kaunnerlmtte in the first or raw smelting, ia as follows. 
 
 * BUchofi O^emiQAl aad Pbyiical Qeolpg/, 11, 235. 
 
 i 
 
 » 
 
 n't 
 
 I 
 
 ■i 
 
ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 
 
 13 
 
 Silica 48.22 
 
 Alumina.. ,. , 16.35 
 
 Protoxide of iroa - .10.75 
 
 Lime 19.29 
 
 Magnesia 3.23 
 
 Protoxide of copper 75 
 
 " " zinc 1.2t< 
 
 35.28 
 
 99.85; 
 
 According to P'attner, tlie melting point of these slags is about 
 1400 ^ Centigiaile.f If wc suppo8(3 that the increase of tem- 
 perature downward in the earth's crust progresses at the rate of 
 1 ° C. for every 100 feet, the thickness of the earth's crust may 
 be calculated as follows. The temperature of the Mondorff arte- 
 sian well was 34 ® C, at a depth of 2066 feet. If we add 100 
 feet for eacli of the remaining 1366 ® ( 136,600 ft.) — the tem- 
 perature of 1400** would exist at a depth of 138,066 feet, (26j 
 Englisjj, or 22f geographical miles.) However crude and un- 
 certain this method of calculating the thickness of the earth's 
 crust may be, it appears nevertheless to have been almost the 
 only one hitherto employed for that purpose. It seems to have 
 been assumed on all hands that the increase of temperatuie takes 
 place in the ratio of a simple arithmetical progrfssion. Hum- 
 boldi| Hilopts the idea that " granite is in a state of fusion aliout 
 "26 or 30 geographical miles beneath the surface." At another 
 pla('e§ lie states it at '* somewhat more than 20 geographical 
 " miles (21/^ = 25 English)." "45,000 metres= 24 geographical 
 " miles, was named by Elio de Beaumont (Goologie, edited by 
 " Vogt, 1840, T, 32) as the thickness of the solid crust of the 
 '* earth. Bisrhof (Wafuielehre des Innnern unseres Er Ikor- 
 " pers, pp, 271 and 286j estimated it between 122,590 feet and 
 " 130,448 feet, or on the average 21§^ geographical=24^ English 
 *' miles," The average diameter of t!ie earth beins; 6864 miles, 
 it follows from the above estimate, that the thickness of the 
 earth's crust only amounts to about jj-j-th of the radius of its 
 circumference. When \ve reflect on this result, it would appear 
 that this thickness is altogether insufficient to lend to the earth's 
 crust tliat stability which it now possesses. Moreover, there are 
 other estimates than those above quoted, which give to the earth's 
 
 * Kerl. Han<lbucli der Huttenknude, I, 296. 
 
 t Ibid ; I, p. 282. % Koamos ; Ebglisb edition, I, 26. 
 
 § Ibid V, 169. 
 
:^^^^ 
 
 I 
 
 ■h 
 
 V 
 
 I 
 
 ■■c 
 
 I 
 
 IF- 
 
 14 
 
 ORIGIN OP ERUPTIVB AND PRIMARY R0CK8. 
 
 crust a mnch more considerable thickness. Cordier assuming 100*^ • 
 Wedgftwood as the melting point of lava, determined the depth 
 at which everything is in a fluid state, from his observations : — 
 
 At Canneaux, to be 14B English geographical mileSv 
 At Littry 84 do. 
 
 At Decise 64 do. 
 
 And he finally draws the conclusion that the average thickness 
 of the solid crust of the earth cannot well exceed 5G English geo- 
 graphical miles.* Sartorius von Waltershausen's estimate will be 
 referred to when we come to take into consideration the density 
 of the earth. Naumann remarks as follows on the subject : " the 
 *' temperature of the fused lava may certainly in the depths of 
 " the earth be estimated as at least 2000® C. If the increase of 
 ** temperature follows the law of an arithmetical progression, then 
 " such a temperature would be reached at a depth of 200,000 feet, 
 " or nineGerman,(=36 English) geographical miles. But since 
 " it is more probable that the distance corresponding to an in- 
 ♦' crease of 1 ® Centigrade augments with the depth, we arc jus- 
 " tified in assuming a much greater depth, and in supposing it not 
 " at all impossible that the seat of the fluid lava is to be found at 
 " a depth of twenty and perhaps even upwards of thirty geogra^ 
 " phical miles (=80 or 120 English geographical miles,)"f There 
 are not wanting observations to prove that the temperature of 
 the earth^s cnist increases less rapidly towards the interior. Thus 
 from a comparison of several observations, Fox deduced the 
 result that within the first 600 feet, the temperature increases 
 more quickly than in the following 600 feet. Henwood obtained 
 similar results within the first 950 feet, and Rogers found in Vir- 
 ginia a rotable enlargment with the depth, of the space corres- 
 ponding to 1 ® increase. In the artesian well at Grenelle the 
 temperature observed at 
 
 700 feet depth was 20.00' 
 
 1555 
 
 26.42 
 
 C. 
 0. 
 
 The thermometer in the cellar of the Paris observatory shews a 
 constant t«emperature of 1 1.7 ® C. Calculating from this depth of 
 86 feet, the <iistance corresponding to one degree's increase of tem- 
 perature within the first 67*7 feet is 81.6 teet; and within the 
 
 • Naumann, Geognosie, I. 74. 
 t Naumann, Geognosie, I, 67. 
 
 I 
 
I 
 
 1^100®. 
 the depth 
 lions : — 
 
 thickness 
 gliali geo- 
 :c will be 
 
 e density 
 Bct : " tbe 
 
 depths of 
 ncrense of 
 sion, then 
 ),000 feet, 
 But since 
 
 to an in- 
 e arc jus- 
 jing it not 
 e found at 
 ty gi^ogra^ 
 )"f There 
 erature of 
 or. Thus 
 diiced the 
 i increases 
 J obtained 
 id in Vir- 
 i(;e cor res- 
 enelle the 
 
 = 0. 
 = 0. 
 
 ry shews a 
 lis depth of 
 ase of tem- 
 within the 
 
 ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 15 
 
 next V92 feet, 123 feet; which figures plainly shew an increase 
 with the depth of the distance corresponding to 1 ® C. Bis- 
 chofs experiments on the cooling of large masses of melted ba- 
 salt also furnish a very convincing proof that the increase of 
 temperature takes place less rapidly at greater depths. 48 hours 
 after casting a globe of melted basalt, having a diameter of 27J 
 inches, he found it to possess the following temperatures : — 
 
 In the centre 163. 5'=' R. 
 
 45 inches from do <.. 136.0 <=> " 
 
 6.75 " " " 124.9® " 
 
 9. " " 109.8®* " 
 
 These observations also shew with increasing depth a diminution 
 of the rapidity with which the increase of temperature takes 
 place. They by no means furnish us however with secure data 
 upon which to found a calculation as to the thickness of the earth's 
 crust. Like the careful experiments in the mines of Prussia and 
 Saxony, ^ a general law with regard to the increase of tempera- 
 " ture cannot be deduced from them." They are useful in so far 
 as they prove the inaccuracy of all estimates of tbe earth's thick- 
 ness founded u "on the arithmetical progression of the increase of 
 temperature, and justify the supposition of Naumann, that the 
 crust of the earth may have a thickness of upwards of 120 English 
 geographical miles. 
 
 There is however yet another estimate of the thickness of the 
 earth's crust, the consideration of which will lead us to refer to the 
 various views entert lined as to the constitution of the interior of 
 the earth. This estimate is thus referred to by Naumann : " W. 
 '• Hopkins has adopted a peculiar method for the solution of 
 " this problem. By very acute observation and reasoniin^ on the 
 "nutation of the earth's axis, and the precession of the equinoxes, 
 " he finds that these two phenomena must come out with different 
 " values according as the earth is solid throughout, or fluid 
 " throughout, or solid externally and fluid internally ; in which 
 " latter case different thicknC'^ses of the solid crust will proluce 
 *' different results. It is certainly the case that in order to a cor- 
 " rect estimate, the values of two important elements are necessary, 
 " which are as yet unknown, viz., the condensing action of pres- 
 " sure, and the expanding action of such high tempeiatures. 
 " Nevertheless, Hopkins has attempted to answer the question ap- 
 
 * Naumaan, Geognosie, I, 63. 
 
 5 
 
16 
 
 QIUQIN OF SBUPTIVE AND PBIUART BOCKS. 
 
 " proximately, and gAinod the result, Uiat according to the known 
 " values of the nutation and precession, the tliickiief^s of tlic solid 
 " crust cannot he less than one fourth or one fifth of the radius 
 '' of the earth and must at least anoiount to 172 to 215 
 " German geographical miles (==» 688 to 860 English geogra- 
 " phical mile».) Such a thickncs>) of the earth's orust 8««iits indeod 
 " to stand in the necessary relations to the stAbility of the exterior 
 *' surface of the earth, but also almost completely to exclude the 
 " possibility of a communication with the interior of the earth, 
 " which is really so decidedly shewn to exist by varied volcanic 
 " phenomena. Hopkins also adopts the view that with such a 
 " thick cru^t a direct communication is impossible between the 
 " interior of the earth and the surface. In order therefore to 
 " explain the phenomena of volcanoes, he supposes the existence 
 " of very large cavities herci and there within the solid crust, 
 " which are filled with easily fusible materials, still in a liquid 
 " state, and which resemble colossal bubbles, enclosing whole seas 
 " of fused substance.* Elie de Beaumont and others, on the 
 other hand, entertain the view that spaces were formed between 
 the solid crust, and the fluid c(?ntre which, at least in earlier geolo- 
 gical periods, caused pariial depressions of the earth's crust, and 
 which are still to be consiJercl as the real laboratories of volcanic 
 activity. 
 
 Somewhat allieil to Hopkins's supposition is Bunsen's theory, 
 which rests upoti certain ascertained facts with re<i;ard to the com- 
 position of igneiHis rocks genir-rally, but more especially to that of 
 lavas. Bunsen supposes the existence in the interior of the earth 
 of two enormous reservoirs of fused matter having each a differ- 
 ent composition, and from the amalgamation of which all the 
 known varieties of trachyticand doleritic rocki^ result. This theory 
 is based upon two series of analyses of Icelandic lavas^ the one 
 comprising, accordingto Bunsen, those richest in silica (trachytes), 
 the other those containing the largest amount of ba.ses, (trap 
 rocks, basalts and basaltic lavas). The first series of analyiMs com- 
 prised those of the following rocks : — 
 
 1. Trachyte from Baula. 
 
 2. Do from Kalmanstunga. 
 
 3. Do from Langarf jail near the Geyser. 
 
 4. Trachyte from Arnar Knipa on the Laza. 
 
 5. Do from Falklaklettur near Kalmanstunga. 
 
 • Naiwoaun, Gepgno^ie, 1, 15. 
 
 I 
 
 I 
 
ORIGIN OP ERUPTIVB AND PRIMARY ROOKS. 
 
 17 
 
 6. Trachyte from Krabla. 
 
 7. Obsidiun from Krabla. 
 
 1. 2. 3. 4. 6. 8. T. 
 
 Silica 75.91 77.92 75.29 78.95 76.42 7(>.38 75.77, 
 
 Alumina 11.49 12.01 12.94 10.22 9.57 11.53 10.29. 
 
 Ferrous oxide 2.13 1.32 2.G0 2.91 5.10 3.59 3.85. 
 
 Lime 1.56 0.76 1.01 1.84 1.53 1.76 1.82. 
 
 Magnesia 0.76 0.13 0.03 0.14 0.20 0.40 0.25. 
 
 Soda 2.51 4.59 2.71 4.18 5.24 4.46 5 66. 
 
 Potash 5.64 3.27 5.42 1.76 1.94 1.88 2.46. 
 
 100.00 100.00 100.00 100.00 100.00 100.00 100.00 
 
 The mean of these analyses is : 
 
 Silica 76.662 
 
 Alumina 1 1.15o\ 
 
 Ferrous oxide 3.07 1 1 
 
 Lime 1- 4691 23.338 
 
 Magnesia 0.274( 
 
 Soda 4.178 
 
 Potash 3.196J 
 
 100.00. 
 
 This Bunsen assumes to be the composition of tlie normal 
 trachyiic nm**s, which occupies one of the reservoirs of his tlieory. 
 The second series of analyses comprised those of the following 
 rocks : 
 
 1. Trap rock from Esiaberg. 
 
 2. Trap from Vidoe. 
 
 3. Light tine grained basaltic rock from Hagafgell on the right 
 
 bank of the Thiorsa. 
 
 4. Basaltic rock from Skardsfjiill. 
 
 5. Lava from an old stream of Hecla. 
 
 6. Rock from the precipice of Almanoagjo near the lake of 
 
 Thingvalla. 
 
 1. 2. 3. 4. 6. 6. 
 
 Silica 50.05 47.48 49.17 47.69 49.37 47.07. 
 
 Alumina 18.78 13.75 14.89 11.50 16.81 12.96. 
 
 Ferrous oxide... .....11.69 17.47 15.20 19.43 11.85 16.65. 
 
 Lime 11.66 11.34 11.67 12.25 13.01 11.27. 
 
 Magnesia 5.20 6.47 6.82 5 83 7.52 9.50. 
 
 Soda 2.24 2.89 0.58 2.82 1.24 1.97. 
 
 Potash 0.38 0.60 1.67 0.48 0.20 O.fiS. 
 
 100.00 100.00 100.00 100.00 100.00 100U)0. 
 
 'Si 
 
 ■M 
 
f 
 
 18 
 
 ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 
 
 The mean of these analyses is : 
 
 Silica 48.473 
 
 Alumina / 14 781 
 
 Ferrous oxide I 1 5383 
 
 Lime ) 11 .800 SI.628 
 
 Magfnesia J 6.890 
 
 Soda / 1 .957 
 
 Potash \ 0.651 
 
 100.000 
 
 This Biinsen asfiiimcs to be the composition of tlie normal 
 pyioxenic mass, which fills the second supiiosed reservoir of igne- 
 ous fluid material in the centre of the earlh. lie further argues 
 that all volciinic rocks, that is to say rocks bnlonf^ing to the 
 trachytio, basaltic or lava eruptive formations, may be regarded 
 as mixtures of these two fluid materials, and shews that after 
 merely determinin*; how much silica they contain, it can bo 
 ascertained by calculation in what proportions these two materials 
 from the diff'«rcnt reserroirs are present. With regard to this 
 theory Saitoiius von Wakershausen remarks: "It is evident 
 "that this average (that of the normal pyro.xonic mass) can 
 "just as little be regarded as the limit on the basic side, as the 
 "so called normal trachytic average on the other. Nor is it 
 ** apparent why the above-mentioned six analyses only were used 
 " in computing the average, while others, such as lava from Thiorsa, 
 "and trap rork from Esla were neglected."* 
 
 Mr. Sterry Hunt, who as we shall see, rejects altogether the 
 theory which derives the eruptive rocks from a portion of the 
 primitive fused mass of the globe, and supposes them to consist 
 of altered, fused, and displaced sediments, (Can. Naturalist, Dec. 
 1859], remarks, with regard to Bunsen's hypothesis, that tlio cal- 
 culated results as deduced from the volcanic rocks of Hungary 
 and Armenia, often differ considerably from those obtained by 
 analysis ; a result which will follow, when as is often the case, dif- 
 ferent triclinic feldspars replace each other in the pyroxenic rocks. 
 He also shows that the composition of certain eruptive rocks, 
 like phonolites, (which are highly basic, and yet contain but little 
 lime, magnesia, or iron-oxide) is such that they cannot be derived 
 from either of the magmas of Bun sen. 
 
 • Feber die vulcanisclie Gesteine in Sicilien and Island, and ihre 
 ubmarinc Umhildung ; Oottingen, 1853. 
 
 M 
 
1 
 
 ORIGIN OF EK-.l'TIVE AND PRIMARY ROCKS. 
 
 19 
 
 3 
 
 G S1.628 
 
 normal 
 of igne- 
 
 argucs 
 r to the 
 regarded 
 hat after 
 t can bo 
 in atari als 
 rd to this 
 s evident 
 nass) can 
 de, as the 
 Nor is it 
 were used 
 n Thiorsa, 
 
 Tether the 
 ion of the 
 to consist 
 •alist, Dec. 
 at \}\Q cal- 
 r Hungary 
 jtained by 
 e case, dif- 
 cnic rocks, 
 tive rocks, 
 11 but little 
 be derived 
 
 lid, und ibre 
 
 Naumann quietly remark'* that the theory of the two separate 
 reservoirs is surely not yet sufficiently proved, and characterises Von 
 Waltoishausen's theoryof theconstitutionof the interior of the earth 
 as more natural, and more in accordance with our knowledge re- 
 garding the probable condition of the earth's centre.* This theory, 
 which the author first promulgated in the work from which we 
 have just quoted, deserves to be bettor known. It is principally 
 founded upon certain reasonings deducible from the density of 
 the earth, and for this reason a recapitulation of what is known 
 concerning this point may not be inappropriate hero. 
 
 In 1770 Hutton and Maskelyne determined tlie density of the 
 earth from the httraction exerted on the plumb line by the mass of 
 the mountain Schiehallion in Perthshire. Assuming the mean of 
 specific gravities of the three principal rocks, of which it consists, 
 viz., mica slate, limestones, and quartzite, to be the density of the 
 whole mass, they calculated from their experiments the density of 
 the earth to be 4.713. 
 
 The density of the earth has also been determined from observa- 
 tions on the oscillations of the pendulum on high mountains. In 
 this way Carlini found from experiments on Mount Conis the den- 
 sity of the earth to be equal to 4.37, which value was however 
 raised by Schmidt to 4.837, by correcting an error in Carlini's 
 calculations. 
 
 The most exact method however yet applied towards deter- 
 mining the density of tiie earth is that by means of the torsion 
 balance .nvented by the Rev. John Mitchell, and used after his 
 death by Cavendish. In 1798 this philosopher communicated to 
 the Royal Society the result of his experiments with this appara- 
 tus. From seventeen sets of experiments he deluced twenty- 
 three results, from the mean of which he computed the density of 
 the earth to be equal to 5.48. Bailly, correcting an error in 
 Cavendish's calculation, makes it 5.45. Schmidt, likewise, after a 
 revision of Cavenilish's computations, alters the result of these to 
 6.52. In 1837, Reich of Freiberg performed a series of experi- 
 ments with the same apparatus, much improved in various par- 
 ticulars. Fifty-seven experiments were made in all, from which 
 fourteen results were deduced,the mean of which makes the density 
 of the earLh equal to 5.44. In 1848 Baily, at the rei]uest of the 
 Astronomical Society, undertook to repeat Cavendish's expv'riments. 
 
 * Lebrbucb, ii, 1101. 
 
:iO 
 
 ORWIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 It was not however until 1841 that thu npparatns wrr mofMflod 
 and iniprove»i to suiJi an extent as to j^jive the most RiiiNfai'tory 
 ♦eaults. The cxperiniuntii with the poiftjctetl apparatuH were 
 •oontiniicd till M'«y, 1842, when the rofliiit was amved attimt the 
 moan density of ilii; earth is 5.00. From this enunn'ration of all 
 the experiments which have been made for the detcrminaiion of 
 the mean density of the earth, it will be evident that the result as 
 given by Baily, w one of the most um^quivocally estiblishod 
 •Bcientifio facts. Not only is there ((ionsidoring, the dittVrent times 
 and cirfumstancos when they were instituted) a Burprisinsjf coinci- 
 dence ill the reHiiltH obtained by (he torsion balance, but these are 
 confirmed in the mean by the results obtained from the less 
 «ccuriito methods Hist described. 
 
 If wo compare tim mean density of the earth, as found by Baily, 
 with tlie specifiii ginvities of a few well known minerals, we find 
 that it e<|nals the density of copper glance, and exceeds that of 
 magnetic iron or<', in»n pyrites, varii'giited copper ore, and copper 
 •pyrites. If wt- moreover compare it with the specific gravities of 
 these minerals or rocks which constitute the great bulk of the 
 «artli's crust, wo find it to possess twice as groat a density. The 
 inference is unavoidable that the centre of theearih is mu(rh more 
 dense thnn its crust, and is also possessed of a higher d-nsity than 
 that of tho earth's whole mass. This conclusion has, nevertheless, 
 teen received by many with grave doidits. It has even been sup- 
 pose 1 that the increased density at the earth's contio is attribu- 
 table to the incrt'HRcd density which the substances there existing 
 •cquire from the enormous pressure of the superincumbent mass. 
 -This explanation rests upon the groundless su[)position that 
 «oIi(l» may bo compressed to an indefinite extent. It further ne- 
 glects the very essential circumstanue that the attraction exercised 
 on any material point in the interior of the earth is oidy exerted 
 fcy that part of the earth which lies within the 8pheri«!al surfiice 
 passing throuiih the given point, and that the mass of the earth 
 outside of this surface exercises no attracting influence oti it. 
 Since therefore the weight of a body is determined by the sum of 
 the attracting forces acting on it, it follows that the weight of one 
 and the same l>ody must be less in the interior of the eartli than 
 on the surfnce.* Moreover, it is very certain that an extraordi- 
 narily high temperature exists in the interior of our planot, which 
 
 be8- 
 
 * Xaumann, Lebrbucb, i, 40. 
 
1 
 
 moflifiod 
 ii»t'ai!tory 
 ituH were 
 
 tliHt the 
 on of all 
 nation of 
 
 result as 
 fttiililishod 
 rent times 
 ng coinci- 
 
 ihcsoare 
 
 the less 
 
 by Bally, 
 U, we find 
 Is tliat of 
 in<l copper 
 iirnvities of 
 julk of the 
 isity. The 
 mucii more 
 •nsity than 
 everthelese, 
 n been sup- 
 in attribu- 
 Dre existing 
 ibcnt mass, 
 sition that 
 further ne- 
 »n exercised 
 >nly exerted 
 rical surface 
 »f the earth 
 ence ox\ it. 
 / the sum of 
 jiy^lit of one 
 ! earth than 
 n extraordi- 
 anot, which 
 
 I 
 
 ■i 
 \ 
 
 OllIQIN OP BRUPTIVB AND PllIMAHY ROOKS. 21 
 
 must cause the bodies exintinoj there to expand, and wliich must 
 thus iieuiraliHe much uf tlie comproAHiou oxuruiHed on tliUHe bodies 
 by the mnsst'N lyin<r above them. Finally, it «Hein» tiiat tlie com- 
 pressinj; powers of the Hupcrincumbent masses have b.-cn Hoincwhat 
 over eHiinuited. The crust of thu earth muHt be re^iinled as a 
 8elf-HU|tportinflf arcli, exorcisinpja prcsure only oti the elastic fluids 
 occurring in it, and not as resting or floating on ilic fluid interior. 
 Tlie latter lias then only to bear the weight of the columuH of lava , 
 which may exist in the interior of volcanoes, and which is certainly 
 not inconsiderable. From these considerations ii wo.ild seem per- 
 fectly correct to suppose that what tlio crust of the earth wants in 
 dciksiiy as compared with the whole mass of the planet, must bo 
 made up by tlie centre. 
 
 Naumaiin finds that assuming the average density of the earth's , 
 crust to be '2'5, and the increase of density to take place accord- 
 ing to arithmt'tical progression, the density of the centre would 
 be 8*6, consequently considerably more than the specific gravity 
 of iron, and almost et^ual to that of cobalt. A similar calcula- 
 tion is the starting point for the theory alrea<iy mentioned of 
 Sartorius Von Waltershauscp. lie finds the mean of the specific 
 gravities of orthoclase, albite, quartz, crystalline limoslono and 
 mica to be 2*00, and assumes this as an approximation to the 
 mean density of the outer crust. Calculating, first, three fifths 
 of the total volume of the earth to possess this specific gravity, 
 he finally computes the density of the centre to be 9 585. He 
 moreover calculates the densities which exist at various depths , 
 beneath the earth's surface. These depths, converted into English . 
 geographical miles, with their calculated densities are as follows :— 
 
 Miles from surface. Density. 
 
 2'66 
 
 34 2-79 
 
 68 2-93. 
 
 103 3-07 Lime. 
 
 137 3-20 Magnesia. 
 
 171 3-34 
 
 206 3-47 
 
 240 s-ea 
 
 27t 3.73 
 
 309 3-85 
 
 343 3-99 Alumina, 
 
 686 515 Icon-oxide. 
 
 1029 .^•••••* 6-29 Tellurium, Chromioia 
 
 i 
 
22 OKIUIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 Uileii flrom itirface. De sftjr. 
 
 KI72 700 Zinc, Iron, Antimony 
 
 17l(j 7.85 Cobalt, Steel. 
 
 2030 1*47 Uranium, Niciicl. 
 
 2403 8'Ott Copper. 
 
 2745 0-31 
 
 80R8 O'Sl 
 
 3433 0-69 Bismuth, Sllrer. 
 
 The theory iimintttinod by Sartorius Von Walteri»hau8cn r«'gard- 
 ing the ctmsiitufion of the earth's interior, (in opposition to 
 Bumhi'd'h hvpothenia of the two soparato reuervoirA of acid and 
 basic molten rocic,) is indicated Dy the above Heries of <;ah;ulatod 
 deiiHitit's. Ilti Hupposes that from the interior of the earth's 
 crust to its centre a gradual increase of density lakes place in the 
 fluid mass, or that this fluid mass in its present condition, as in 
 former u;4;es, consists of a series of concentric layers of molten 
 matter, which are the denser the nearer they approach to the 
 earth's centre. Instead therefore of regarding trauhytic and 
 basaltic lavas as the products of the two separate reservoirs, he 
 considers tliein as the products of two different concentric layers, 
 or as originating from two different levels in the fluid mass, the 
 basaltic lava occupying the lower layer or level, and the trachytio 
 floating above it; the one, both as regards chemioii composition 
 and density, graduating into the other. Von Wuiterslmnsen found 
 the mean s|)ecific gravity of seven different Icelandic trachytes to 
 be 2,524, while that of ten different basaltic lavas amounted to 
 2,911. With thcincreascof specific gravity towards the centre, Von 
 Waltershausun supposes also an increase in the basic constituents 
 of the molten rock, a change from a purely feldspathic material, 
 yielding trachytio r' iks mainly composed of feldspar, to one 
 much richei' in lime, magnesia and iron-oxide, and yielding 
 dolerites consisting of feldspar, hornblende or auc^ite, and in 
 smaller ipiantity magnetic iron ore. He further supposes that 
 beneath this dc.eritic material the quantity of iron-oxide, capable 
 of producing the last named mineral, goes on increasing, and that 
 ultimately a po'nt is reached from which to the centre metallic 
 elements alone exist. In fu?*>f,. reasoning as to the condition of 
 this metallic centre, Von Wait "'^hausftn takes into consideration 
 the intiuence of the supe jjcumbeii; pressue upon the fusing 
 point of the metals. The loUov»"ina is a trans, ation of his remarks 
 on this subject : " For son ^time past Bunsen has devoted his at- 
 ' tention to this subject, and described (in Foggendorff 's Annalen, 
 
 m 
 
 ? 
 i 
 I 
 
 .11 
 
ttaonj 
 1. 
 
 «i 
 
 'i 
 
 I 
 
 
 
 ORKUN OP EKIIITIVE AND PaiMAKY HOCKS. 28 
 
 * 
 
 " Lxxxi, 602) n H<Tio« of experimentn from whir' it, nppears 
 ** Uint tlit^ t<'ni|ii!i'atiirt) of tlio fuHiii^ point of vHri<iUh ^ubitltinces 
 *' iiiur«HKon wiili pn-HMUro. 'I'licse expcririiontJi liavtt it i» trut< only 
 " been iniulc on two crt»ily funiblo organio Hub«tiuic«H ^j •>rmacuti 
 **■ Hnd ptiniffinc. The niulting point of tlio foi-iiii>r is under » 
 •* pre8Hiir(» of 100 ;itinoRpliere» raiocd 2.1° Centijtfriuie, while that 
 *• of panifHnf is laixod 3.0° Centigrade. It cannot Itodoiibicl that 
 '♦ a heavy pn'^HunjactH in a Himiiar manner, allhtnigh pOHnibl^ not 
 " to HUch an iipprcciabie extent, upon HolidifyingnuiHHeHufHilicateB. 
 •* If the point of fiisi'i i of vhe latter, under a preHHinu of 100 atmos- 
 " phoreB, only 'mck hs i<I 1"^ Centigrade, this would still be HiifHcient 
 " to explain uiuoy itiiporttnt points in geology, and e8|)ecially in 
 "the f' riMjitioii o ryHtalline rocks. Although the law of the 
 "dep.'i I,' 'Ai of ilio point of fusion upon pr«'ssiiro is far from 
 " being kno^vn, the observations of liunsen already mentioned 
 " have incite 1 mo to enquire as to what pressure, on the basis of 
 *• the increase of density already mentioned, may be expected to 
 " exist at any given point in the interior of the earth. If we 
 " iraugiiie the whole globe to be in atluid :;ondition, the following 
 " pressures would be experienced at the respective depths men* 
 " tioued. 
 
 Depths in milca. Pressure in ntmuspberes. 
 
 34 17138 
 
 68 .' 34591 
 
 103 63070 
 
 137 72195 
 
 171 92432 
 
 206 113180 
 
 240 1346G0 
 
 274 156840 
 
 309 1 79680 
 
 343 203320 
 
 6M6 471680 
 
 1029 786080 
 
 1372 1 125690 
 
 1 7 16 1468000 
 
 2059 1701500 
 
 2402 2297500 
 
 3088 2441900 
 
 3432 2492600 
 
 "If it is the ca'se that the fusing point of metals (of which un- 
 ** doubtedly the greater part of our planet consists,) increases with 
 ** increasing pressure, then the question arises as to whether under 
 
 1 
 
2i> 
 
 ORIGIN OF ERUPTIVB AND PRIMARY ROCKS. 
 
 " such enormous pressures as those above CBlculated, even with 
 " the liigh temperatures which we have to expect in th« interior 
 " a fluid condition is conceivable. The hypotliesis of a solid 
 *' metallic nucleus in the interior of the earth has nothing con- 
 ** tradictory in it, a!)d indeed the phenomena of terrestrial mag-' 
 " netism would ap|)ear to confirm this view. It is not to be 
 " doubted that the so-called magnetic storms have their seat in 
 " the atmosphere, or perhaps over it. and that the diurnal and 
 " secular variations of the magnetic elements are only to be ' 
 "sought in the exterior solk.1 or soliilifying crust of the earth.' 
 " If the seat of the greater part of the terrestrial magnetic 
 " power is in the earth's crust, then wo must suppose such a dis- 
 " tribution of the magnetic fluid in it, as if on the average eight ' 
 " hard steel bars weighing one pound each, magnetised to the 
 " highest power, were present in every cubic nit'tre. A(rcording 
 " to geological observation, however, we can scarcely suppose the 
 " seat of the magnetic power to rest in the earth a crust, since it' 
 "does not seem to possess either a very great thickness, or »• 
 " very intensive magnetism. According to an approximative oal- 
 " culation which my friend W. Weber has made, a globe of the 
 " hardest steel, magnetised to the highest degree, and having a 
 " diameter of nearly 470 (Euglish) geographical miles, situated 
 " in the centre of the earth, would be able to produce the mag- 
 " netic phenomena which we observe on th8 earth's suiface. In 
 " reality however these suppositions Are not reliable, since we can 
 " neither expect to find hard steel nor a perfect magnetism in 
 *' the centre of the earth. With less favorable circumstances 
 " than those above supjiosed, it would be necessary to assume the 
 " existence of a much larger solid globe in tlie interior of the 
 " earth in order to account for the magnetism on its surface. 
 " The radius of this globe would- possibly extend far beyond the 
 " point at which, according to the calculations already mentioned 
 " a density equal to that of metallic iron exists," 
 
 In whatever degree Von Waltershausen's method of determin- 
 ing the earth's density at its centre, may be looked upon as 
 uncertain, it is scarcely possible to regard his theory of the 
 gradual increase of density as otherwise than very reasonable. 
 Indeed since it is certain thatthe centre of the earth is much more 
 dense than the surface,. it is scaroely possible to conceive how 
 thei increase can take place otherwise than gradually. Mor» 
 oveit Laplace deduced a similax result from his inveatigation* ' 
 
ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 
 
 25 
 
 regarding the decrease of gravity from tlic })(>le to tlie equator. 
 It appears 'lowcver that Sartorius Von Waltershaiisen's estiniate 
 of the average specifn; gravity of the conslitiients of the earth's 
 crust at its surface is too high, since it is well known that the 
 land only occupies one-fourth of the earih's surface, and that the 
 sea has sometimes a d.pth of more than 27,000 feet. It may 
 probably be assumed with some decree of reason that the average 
 spccitic gravity of the tirst fow thousand feet of the earth's crust 
 below the luvel of the sea, does not exceed 1.5. With regard to 
 the metals constituting the earth's centre, it will probably be 
 admitted that they exist there sotnewhat in the same proportion 
 as they occur on the surfa(!e, tluit consefjuently iron constitutes 
 by far the greater portion of the central ma?s. This supposition 
 seems contirmed by the fact that among the gaseous produ(;ts 
 emitted by volcanoes, chloride of iron is very abundant, while 
 traces only of tlio cliloride of lead and copper have been de- 
 tected. Since further, meteoric iron may be supposed to come 
 from bodies having a common origin with our earth, their com- 
 position might be supposed to afford a clue, however slight, to the 
 composition of the metallic centre of the earth. It would there- 
 fare seem not unreasonable to suppose that this centre is mainly 
 composed of metallic iron, combined with copper, cobalt, nickel, 
 lead, and perhaps silver, gold and platinum in comparatively 
 small quantity, jind that its specific gravity may be estimated on 
 account of tliir, ailinixture of heavier metals at 8.0 (Sp. gr. of 
 malleable iron 7.78; cast iron, 7.1 to 7.5.) If we assume 1.5 
 as the density of the earih's surface, and 8.0 as that of its centre, 
 we must also — since the average density of the earth is 5.56 — 
 suppose the existence at the centre, of a globe of metallic matter 
 having a radius of 2245 English geographical uiles. i\ssurn- 
 ing further a gradual increase of density from the surface of the 
 earth to the surface of this metallic globe, we may calculate that 
 at a depth of 132 miles the density of trachytic lava is reached, 
 (2.5), and at 202 miles the density of doleritic lava is slightly 
 exceeded (3.0). According to this calculation therefore the 
 crust of the earth has a thickness of from 132 to 202 miles, 
 a result somewhat exceeding Naumann'a estimate. Calculating 
 in the same way wo further find that from a depth of 202 miles 
 to that of 352, molten rock would exist having a specific gravity of 
 from 3.0 to 4.0, and containing much more basic matter and iron- 
 oxide than any rock now'visible on the surface. At a depth of from 
 
26 
 
 ORIGIN OF ERUPTIVE AND TRIMARY ROCKS. 
 
 352 to 518 miles, substances may exist having a density 
 of from 4.0 to 5.0; such as magnetic iron oro, ilmenitc, copper, 
 iron, and magnetiii pyrites, variegated copper ore, sulphurct of 
 antimony, and perhaps antimonio-sulphurels. From 518 to 705 
 miles in depth, substances may be present having a spocilic gravity 
 of from 5.0 to 6.0 such as iron pyrites, miUerite, and copper glance. 
 Deeper still, and until a depth of 923 mihis, a density of from 
 CO to 7.0 may bo suppose 1 to exist, and consequently arsenio- 
 sulphurets of iron, cobalt and nickel, such as arsenical pyrites and 
 spei^s-cobalt, cobalt glance, and lesseral pyrites to be present. 
 Between this depth of 923 miles, and that of 1187 miles, where 
 according to tlie calculation already mentione^l, tlie surface of the 
 metallic globe may be found, we may suppose a density of from 
 7.0 to 8.0 to exist, and more or less pure arseniurets, sucli as the 
 purest speiss-cobalt, arseniurets of copper and nickel, «.l'c, to be pre- 
 sent. It will be evident that in calculating tlie results above given, 
 I have only been endeavouring to develope Von Waltershausen's 
 theory, and in some measure to correct l.is results. I .«ay conect 
 1 hem, because in one instance assuming the sp. gr. of the surface as 
 2. CO, lie arrives at the result that the thickness of the earth's crust 
 docs not exceed 07 Eiiglisli geographical miles. So far as regards 
 the composition of the various concentric layers deduced from 
 iheir specific gravitie-*, I may remark that I have observed a 
 himilar succession to that above indicate 1, manifest itself in 
 smelting cobalt ore>. This operation is carried on at Modum in 
 Norwav, where on drawing the metal from the furnace there are 
 formed in the crucible receiving it, four diliereiit layers of material, 
 which from the surface downwards, are as follows, viz. : Slag 
 containing about GO per cent, of lime and (xide of iron; 2nd, 
 sulpliurets of copper, iron and cobnit; 3r 1, Aiscniosul))luirets of 
 iron and cobalt, graduating into 4lh, iin|)ure m<itallic iron, mal- 
 leable and C)ntaiiiinj; cobalt. Thy accompanying sketch shows 
 ]):ut of a section of the earth, cxhibiiing the size oi the central 
 metallic globe, the thickness of tlie conticutri.; layers, and of tlio 
 solid crust acconliiig to the above calculations. As to whether 
 the metallic globe in the centre is in a solid state, there would 
 appear to be good grounds for this supposition, because apart 
 from the (consideration that the solidifying point rises with the 
 ]»ressure, it is well known that in m;iny sniclling furnaces, me- 
 tillic iron can accumulate in the bottom, while the sl;i<r maintains 
 its fluidity and runs perfectly free from the furnace. Mr. Sterry 
 
ORIGIN OF ERUniVE AND PRIMARY ROCKS. 
 
 27 
 
 Hunt inclines also to the siippositiiMi tlifit the centre of the 
 earth is solid, although he is of opinion that the fluid matter 
 resting above it is altogether of sodiineiitary origin, and is in a 
 state of igneo-aqueous fusion. He remarks " that beneath the 
 outer cnist of sediments, and surrout)ding the solid nucleus, we 
 may suppose a zone of plastic sedimentary material adequate to 
 
 explain all the plienomnna liitliorto a^ciilh^d t i a fluid nucleus.'' 
 (American Journal of Scioiic.' for May, 1801/) If, further, iron, 
 when fused losos its ma2,'iu't'c power, and the phenomena of mag 
 jictism on the surface of the o:irth can be explained on the supposi- 
 tion that the metallic centre has assume! the s.»lid form, Ihen this 
 supposition would appear to be very rciisonable indeed. It would 
 of course be impossible to assume that Iho metal have not only 
 
28 
 
 ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 solidified but also cooled to siKdi an extent as to be capable of 
 being magnetised to the most powerful degree. On the contrary, 
 we must suppose them to bo still very considerably heated, and 
 consequently to possess but feeble magnetic properties. Accord- 
 ing to Humboldt. " all magnetism is certainly not lost until wc 
 ,' arrive at a white heat, and it is manifested when iron is at a 
 <' dark red heat." * The feeble magnetic power of the metallic 
 globe would however bo amply compensated for by its enormous 
 
 size. 
 
 The possibility of llie oxisteticc of such a metallic centre 
 having been once admitted, the field opened for further reasoning 
 as to the influence which cosmical bodies may exert upon its 
 position, and consequently upon that of the earth's centre of 
 gravity, is very wide indeed. That these changes may afiect the 
 hhenomena of volcanic eruptions, I shall endeavour to shew in 
 Part II. of this pajier. In the meantime it may bo remarked 
 that there exists a decided covinection between magnetic, and 
 volcanic phenomena. In the year 1*767, Bernouilli observed 
 that during an earthquake the inclination decreased half a degree, 
 and Father de la Turre remarked that during an eruption of 
 Vesuvius the declination varied several degrees. On the 18th 
 April, 1842, at ten minutes past nine, Kreil in Prague observed 
 that the needle received a verv sudden stroke, and the same 
 oscillation in the same direction was observed at the same instant 
 by Cella in Parma, and Lamont in Munich. Sliortly afterwards 
 it was ascertained that exactly at the same minute a violent earth- 
 quake had been felt in (ircece.f From the irregularities in the 
 course of the magnetic curves, Lamont regards it as in the high- 
 est degree probable that the seat of terrestrial magnetism is to be 
 sought in a compact nucleus which lies under the earth's crust' 
 Muller is of opinion that the magnetic variations and oscillations 
 can be most simply explained by considering terrestrial magnet- 
 ism as dependent on electric currents which pass through the 
 nucleus in ever varying direction and intensity. | 
 
 That the magneti; variations stand in connection with the 
 movements of certain of the iieavenly bodies is a well ascertained 
 fact. Sabine came to the conclusion that the disturbances bclonfj 
 
 " Humboldt's Cogmos, English Edition, I, 183. 
 t Miiller'a Kosmische Physik, p. 497. 
 t Ibid 98. 
 
ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 20 
 
 "S! 
 
 "to a special kind of periodically recurring variations, which 
 '• follow recognizable laws, depend upon the position of the sun 
 *' in the ecliptic, and upon the daily rotation of the earth round 
 " its axis, and furtlier ought no longer to be designated as irreg- 
 '♦ ular, since we may distinguish in them, in addition to a special 
 ** local type, processes which affect the whole earth."* The 
 hypothesis of a metallic centre would seem to be capable of form- 
 ing the connecting link between the magnetic and astronomical 
 phenomena here referred to. The relation of the sun lo the earth 
 and the revolution of the latter on its axis, wouM naturally effect 
 a change in the positition of the metallic globe in the centre of 
 the earth, which change might alter the direction of the electric 
 currents Uirough the earth's crust, and these again the position of 
 the needle. Thus it seems not at all unreasonable to adopt the 
 theory of a metallic centre, since it alone is capable of afford- 
 ing a solution of many problems in geology, magnetism and as- 
 tronomy, and since it is capable of uniting harmoniously and ex- 
 plaining the most varied natural phenomena. 
 
 II. The ERUi'iivE formations. 
 In referring to these formations, it will be impossible altogether 
 to avoid mentioning many matters which are very generally 
 known regarding them. Still the connection of eruptive rocks on 
 the one hand with the constitution of the interior of the earth as 
 adverted to in the last chapter, and on the other hand with certain 
 s aty modifications of themselves, will be kept in view as much as 
 possible. The rocks of these eruptive formations possess, as is 
 well known, characters which distinguish thera sharply from rocks 
 of sedimentary origin. While the latter have been made up of 
 the debris of rocks pre-existing on the earth's surface, the eruptive 
 formations have derived their material from beneath the earth's 
 crust. Hence they have been respectively termed by Humboldt 
 exogenous and endogenous rouks. The eruptive rocks are more 
 or less crystalline, generally but not always unstratifiiid. The sedi" 
 mentary rocks possess opposite characters. Each eruptive rock 
 is in a high degree homogeneous, and shows nearly the same char- 
 acters and composition throughout its whole mass. This is much 
 less the case with sedimentary rocks. The eruptive rocks occur 
 ^n very irregular forms, as enormous irregular masses, (typhonische 
 stocke) covers or wvps (Kuppen or Decken), veins, streams and 
 
 • Ilumboldfs Cosmos, v, 138. 
 
30 ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 do. 
 do. 
 
 do. 
 
 do. 
 
 layers. Sedimentary rocks occur only in the latter form. Erup- 
 tive rocks are totally destitute of fossils, and their ages are deter- 
 mined by tbo relations of contact which exist between them and 
 Bedimentary rockt*. Fossils constantly occur in the latter, and con* 
 jstituto the principal means of determining their age. Eruptive 
 rocks resemble in the mode of their formation the slags which 
 run out of smelting furnaces ; sedimentary rocks the slimes depos- 
 ited in stamp-works and allowed to consolidate. 
 
 The eruptive formations have been arranged in the order of 
 their antiquity by Naumann as follows : 
 
 1. The granulite formation. 
 
 2. The granite do. 
 
 3. The syenite do. 
 
 4. The greenstone do. 
 
 5. The porphyry do. 
 0. The melaphyr 
 v. The trachyte 
 
 8. The basalt 
 
 9. Tlie lava 
 
 This arrangement is however general and approximative. Xot 
 only do the rocks of these formations in their lithological charac- 
 ters giaduate into each other, but the latter part of one formation 
 may have been erupted simultaneously with the earlier rocks of 
 the succeeding one. Thus trachytes and basalts are almost of 
 contemporaneous origin, and porphyries have been protruded 
 through the earth's crust in the same periods as certain greenstones 
 and melaphyrs. I .«>hall therefore class several of these formations 
 together and refer to them in the following order: 
 
 1. Iraehyte, Basalt, and Lava. The volcanic formations of 
 Nanmann. 
 
 2. Porphyry, greenstone and molaphyr, i The plutonic forma- 
 
 3. Granite, syenite, and granulite, j tioas of Naumann. 
 
 Trachyte, Busalt, and Lava, T have already adverted to the 
 distribution of volcanoes as constituting a proof of the existence 
 of a molten zone betwixt the central metallic globe and the crust 
 of the earth. I do not deem it necessary to enlarge much upon 
 this point. As Naumann remarks: " Volcanoes exist in every 
 part of the earth, under ».very latitude, under the equator and near 
 to the pole?, in the torrid as well as in the temperate and frigid 
 zones. TIk'v are contined to no (.limate, becauso in Iceland 
 
ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 31 
 
 Kamschatka and the Aleutian Island, between a latitude of 50^ 
 and 60° they exist as numerously as in the Sunda isles, Galapa- 
 gos, and in Quito between 0° and 10° lat. But we find them 
 especially frequent on the coasts of continents or rising out of the 
 depth of the ocean, proving that there the conditions are espoci- 
 ally present which are necessary to their development and activity. 
 From all this we may conclude that the material cause of vulcan- 
 ism is present everywhere beneath the earth's crust, although it 
 may only have been able to break out along certain lines a.id at 
 certain points." By means of volcanoes and the subterranean 
 canals connected with thera, a communication is established be- 
 tween the molten zone beneath the earth's crust and the atmos- 
 phere. This communication is liable to bo interrupted by vari- 
 ous circumstances, and when this is permanently the case the 
 volcano is extinct. But even the active volcanoes are far from 
 being continually in a condition of violent eruption ; their usual 
 activity is rather of a very temperate character, and F. Hoffmann 
 very correctly remarks that the energetic eruptions are more the 
 exception than the rule. Volcanoos in a state of rest exhale steam 
 and other gases, and it is even the case that a ipiict etiusion of 
 lava may take place unaccompanied by any extraordinary phe- 
 nomena. GeneniUy however the ascent of the lava in the canal 
 and crater of the volcano is the immediate cause of all the sublime 
 eflects and terrible dtivastution?', which accompany and follow vol- 
 canic eruptions. It is still a matter of doubt among philosophers 
 as to what is the real cause of tiie ascent of the lava from its home 
 in the depths of tlio earth. The oldest hypothesis is that which 
 attributes tlio force which expels the lava to highly compressed 
 steam, resulting from the access of Avater, and especially of sea 
 water, to the regions tilled with igneous llui<i beneath the earth's 
 crust. In later times this view has been adopted by very many 
 philosophers such as Gay Lussac, Von Buch, x\ngelot, Bischot^ and 
 Petzholdt. On the other hand, Humboldt does not at all regard 
 the problem as completely solved, ^^ anil Naumann does not consid- 
 er it probable that the expansive force of the steam derived from 
 sea-water is the cause of the ascent of the lava, although he con- 
 siders it as quite certain, that sea and other water obtains access 
 through the eruptive canals of volcanoes to very great depths 
 and on the ascent of the lava plays a very important part in the 
 phenomena of volcanic eruptions. Naumann's view so far as re- 
 
 
 Cosmus I, 243. 
 
82 
 
 OBiaiN OF ERUPTIVE AND PRiMAttY ROCKS. 
 
 garJs tbc part played by water seoms very reasonable. We caii 
 readily conceive that it would bo (iitticult lor water, even uiuler 
 considerable pressure, to obtain access by means of fissures or 
 otherwise through the solid crust of the earth to the melted mass 
 beneath. As previously remarked, it would bo impossible for it to 
 penetrate the highly heated rocks constituting the inner part of 
 the earth's crust. But it would seem very possible, especially in 
 those volcanoes situated on the coasts of continents, for water to 
 obtain access to great depths in the craters and subterranean 
 canals. As to the cause of the rise of lava in these, Naumann 
 propounds the following theory : 
 
 *' The solidiCed crust encloses the fluid interior of our planet, 
 and at their junction the same solidifying ])roceE8 by wliich the 
 crust of the earth was formed, must still be going on. Because 
 however imperceptible the radiation of the internal lieatmay now 
 be, it still continually takes i)lace although m a lesser degree ; and 
 it cannot be doubted that on the inner side of the earth's crust fluid 
 matter is continually assuming the solid form. It is indeed the case 
 that the greatest number of fluid bodies experience a diminution of 
 their volume, and only a few of them, such as water and bismuth, 
 expand while solidifying, but we must reflect that the relations as 
 to density of the bodies existing in the great depths of the earth 
 M'here vulcanisra has its seat, must be essentially different from 
 those Avhich they possess on the surface, where we can experiment 
 with them. The pressure of the superincumbent masses must com- 
 press the materials existing at these depths. But fluid bodies are 
 gifted with a much greater degree of compressibility than solid bo- 
 dies, and therefore it can easily happen, that the most and per- 
 haps all fused material which solidities on the inside of the earth's 
 crust experiences in this solidification an increase iu its volume. 
 The unavoidable consequence of this can be no other than that 
 daring this slowly progressing solidification a ditniiiution of the 
 capacity of the earth's crust takes ])lace, that consequently the 
 the space enclosed by it and filled with fused material is contrac- 
 ted. The next consequence will be, that a part of the fluid ma- 
 terial will be prcssinl up sometimes through one and sometimes 
 through anctlier volcanic canal, uuiil the weight of the column of 
 lava oqualiz'^'S the pressure in the interior. In this way the first 
 conditions are given by means of which vol(!anicerui)tious become 
 possible.'"* Tiie ol.jcctions to this theory lie in the following 
 
 • Lehrbuch I. 289. 
 
ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 83 
 
 coneiderations. The difference in the compressibility of Hiiid and 
 solid bodies docs not seem to bo very considerable. Water is 
 but slightly compressible. According to Oer.-^tedt, the compres- 
 sion produced by a prossuro of 2000 atmospheres amounts ouly to 
 l-12tii.,'l* and one would suppose that fluid lava would be oven less 
 compressible than water. The decrease of compressibility which 
 may accorap vny soiiilificalion would therefore seem inadequate to 
 the production of suedi stnpenduous effects as are ol)scrvablo dur- 
 ing volcanic eru|)tious. Further, if this were the cause of the 
 ejection of the lava, the latter would be i>oured forth only by vol- 
 canoes of inconsiderable height, but by these simultaneously. Its 
 ejection would also keep pace with tlic v^ry slow and gradual 
 solidification in (he interior, and violent volcanic paroxysms would 
 not occur. 
 
 SartoriuB Von Waltcrsliauscn likewise assumes that expansion 
 takes place, but he does not attribute it to the mere difference in 
 the compressibility of the igneous material before and after soli- 
 dification, lie supposes that the expansion takes place in the act 
 of crystallization, i. e. while the various minerals form and separate 
 themselves from the fluid magina.f He fails however to adduce 
 any conclusive evi lence in support of ti)is supposition, which it 
 might be j)ossible to s'lstain, in the event of its being possible to 
 show that melted rock rapidly cooled to :i line grained crystalline 
 mass, had a l«'sser specific; gravity than .lie same slowly cooled 
 and distinctly crystal liz«xl. lie indeed shows that the specific 
 gravities of the minerals which result in the cooling of igneous 
 rocks, are invaiiably less than those whi(di result in calculating 
 their spocilic gravit'es from the (|uantitics and densities of their 
 constituents; as the following; instances show : — 
 
 Density, 
 by experiment, from calculation. 
 
 1. Anorthitcfrom ScMjall 2.700 3.225 
 
 2. Labradorite from Kgersund 2,705 3.212 
 
 3. Orthoclase from Haveno 
 
 4. Augite from Monte Kusso 
 
 5. Hornblende from Allna 
 0). Enorlish crown rf]ii?f' 
 
 7. Guinan<l, Flint glass 
 
 8. Bohemian glass 
 
 2.555 
 
 2.S8G 
 2.81)3 
 2.487 
 3.770 
 2.390 
 
 2.935 
 3.208 
 3.447 
 2.721 
 5.640 
 2.735 
 
 • Gmeliii, Hand-book of Chemistry, II. 62. 
 t Uber (lie Vulcanishe Gcstcinc, etc., y. 333. 
 
34 
 
 OUKJIN OF EULTTIVE AND TRIMARY ROCKS. 
 
 But lliis (lix's Dot prove tliat n hwA silicalo, tlio constituent* ot 
 which (iro .ilready in chi'iiiii'jil combirmtiou with eacli other, ex- 
 porieru't's a diniimitioii of density or increase of vohinio in cool- 
 ing and cryatJiiiiziiiL!;. The only instance of the cooling of 
 a fused iiilifat*', which lias been made the subject of observation 
 80 far as ro<;arils density, is the formation of Reaumur's porcelain 
 from glasSjliut this goes rather to prove the opposite of Von Walters- 
 hauRon's theory. Many kinds of gl;i>is, after exj.osurc for several 
 hours to a heat at wliich they be(^ome soft, pass into a condition 
 resembling porcelain, become opaipie, doubtless from the separa- 
 tion of fine particles, whose compvMitiori dilfers from the mass. 
 The resulting Jtojiumur's porcelain is speiitically heavier than 
 the glass from which it is prepared. Moreover, this substanco 
 when again fused and r((piiUi/ voolod yields an enamel, the specific 
 gravity of which is to that of the substance before fusion as 2,62,5 
 is to 2,801.* From this it would appear that instead of an increase 
 a diminution of volume takes places in the slow cooling or crya- 
 tallizatioJi of fused silicates. 
 
 If we reject both of the hypotheses just mentioned, the only expla- 
 nation lett, whereby the ascent of the lava column may be account- 
 ed for is that which is regarded as the cause of the more wide- 
 spread earthquakes, viz. the tluctuaiions of the surface of the fluid 
 interior of the eavth.t While those earthquakes which occur 
 simultaneously with volcanic eruptions, and in volcanic districts, 
 may be considered as a conso(juence of the lava rising in the 
 volcano, the same can scarcely be said of those eartlupiakes which 
 occur in the midst of continents far distant from any volcanic 
 region. According to Naiimann, the most probable cause of these 
 "plutonic" earthquakes is '"a Hiictuiition of the surface of the 
 "fluid kernel of the earth, commencijig from aline or a point. 
 " and progressing according to the laws of the motioti of waves." 
 The cause of such fluctuations he leaves undecided, but in com- 
 menting upon von Iloil's, Merian's and Perrey's investigations as to 
 the greater frequency of eartlKpuikes in certain seasons of the year 
 he proj: ands a question, the consideration of which would seeuj to 
 yield tlu most important results. The investigations referred to 
 established the fact that in the northern hemispheres earthquakes are 
 of greater frequency in winter than during any other season. Von 
 
 Hoff found that of the 115 earthquakes which,during the ten years 
 
 • Gmelin III, 385. 
 
 t Naumaiin : Lehrbuch, I, 291. 
 
ORiaiN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 3.J 
 
 from 1821 to 1830, hiulhecii oxporioncoJ in Umt part of Europe 
 lying north of tlio Alp.s, Jl Im.l occiiirruil in sinniuer, lit in 
 autumn, 43 in winter, an.! 17 in sprinfj. In t!iy sanio way Mcrian 
 arranged all tlio earilujuakes wliieh liad U-en observed in Baslo 
 up to the eml of 1830, with t!io foNowing results: 
 
 Suninier 18. 
 Autumn 39. 
 Winter 41. 
 Spring 22. 
 The most important statistics of tliis character have however 
 been furnished by Porrey of Dijon, who see.ns to have given special 
 consideration fo this Hul-je<;t. He has chissiHed, according to the 
 leasons of the year, 2,979 oarth.iuakes, which have taken place in 
 Europe and the immediately adjoining parts of Africa and Asia 
 from the year 300 to the year 1844, and found: 
 053 to have taken place in summer 
 "705 " autumn 
 
 Oil " winter 
 
 710 
 
 spring 
 
 The maximum fails in the coldest and the minimum in the 
 warmest season of the year, while in spring an I autumn the num- 
 bers arc almost e(jual. Natmiann considers that these observatioii* 
 almost conclusively prove that "at least in Europe and the coun- 
 '' tries innncdiately bordering on it, autumn and winter must 
 "bo regarded as the seisons in wliirh earlii(|U:ike3 most frerjuent- 
 '' ly occur." He adds that it is ditticult to tind a satisfactory expla- 
 nation of tills fact, that the cause ought perhaps to be sought for 
 more in cosmical than in meteorological relations, and finally aska 
 •' May not the position of the earth in the lointcr, ie, inthepoi'ihe- 
 lion exercise an iijluencef^''^'^^ This question ho leaves unanswered, 
 contenting himself with declaring that the mere difference of tem- 
 perature in the seasons of the year can not explain the matter. 
 If, as is supposed in the first part of this paper, thuro exists in the 
 interior of the crust a central metallic globe surrounded by a fluid 
 zone, it is (]uite reasonable to suppose that the former may be influ- 
 enced by the heavenly bodies, that it is attracted by the sun and 
 moon, and tliat theattraction exerted is the more powerful thenearer 
 these bodies approach the earth. Since the sun is nearest 
 to the earth in the winter, there would appear to bo grounds 
 for attributing earthquakes partly to the attraction exercised 
 
 • Lolirbucb, I, 213. 
 
86 
 
 ORIGIN OF ERUI'TIVE AND I'RIMAllY ROCKS. 
 
 by tlie sun upon tlu! Iluid inlorior, and tlio cnnsO(|Uflnt pres- 
 Bure exccroisod by llio latter on tlio oiirtb's (Tust. It moreover 
 appoiirs from invostii^atioiis nm<lo by I'crroy stibsoquent to those 
 ftltovo inflntionol, lliut llio moon also fXiui-i-^eK an innuenco.* 
 
 (iucnstctUf thus refers to the hitter iiivesti^'ations: " A. I'orrey 
 "liRs found from 7000 observations durinii; the first half of the 
 •' present century tliat earthquakes are much more frequent in the 
 "conjunction and opposition of the moon than at other times; 
 " more frequent, wlien the moon is near the earth than wlien it is 
 " distant, /nore frequent in the hour of its passage through the 
 '* meridian than at any other. Krom this it wouKl appear, that 
 "the moon is not without inthience; that it occasions tides in the 
 "central lava in tlie same manner as in the ocean, which tides 
 " press against the eartli's crust and seek an outh)t." The latter 
 part of this quotation seems to contain tlie explanation least liable 
 to objection, of the rise of the lava in volcanoes. Not only may 
 plutonie and volcanic earthquakes bo attributed to this cause, but 
 Volcanic eruptions aho,and with equal justice. If we adopt this 
 explanation it is easier to comprehend why the lava should press 
 forth at one volcano in preforcnce to another, or burst open tho 
 obstructed canals of extinct volcanoes rather than seek an outlet 
 through tho vents already existing in the earth's crust. 
 
 Having thus discussed the various explanations of the cause of 
 the rise of the l.iva in volcanic canals, the phenomena which attend 
 volcanic eruptions may next be adverted to, with the view of 
 ascertaining the origin of certain volcanic products. The lava 
 gra lually ascending from the depths of the earth, comes in the 
 upper part of the canal, and in the crater, into contact and conflict 
 with the water which has found its way down from the surface, 
 and which may have collected in siibterranean reservoirs, or merely 
 saturated the side walls of the vent. The water is by the heat 
 of the l;iva resolve^] into steam, which then forces its way through 
 the fluid to the RuriMCc, when the bubbles containing it explode. 
 A similar phenomenon may be observed on a small scale at blast 
 furnaces, when the slag runs out of the breast and over a place 
 upon which water had been previously thrown. The slag boils up 
 until it cools and becomes too stitt' to allow of the passage of the 
 steam. This production and escape of steam in the craters of 
 volcanoes takes place with a violence and intensity of which tew 
 
 • Bronn's Jahrbuch, 1855, 72 
 t Epochen der Natur, p. 812. 
 
ORIGIN 01-' EUiniVK AND I'KIMAUY UOCkd. 
 
 87 
 
 but oyo witiiossos ciui tonn iiny idoii, S»irtori\i!» Von WnIloiHlmu- 
 sen ihurt'lescribos h vulcanic ciupi ion, principally in relation loiho 
 varit)us producls fonniMJ by it : " During an eruption tlif* nicitud 
 "m.itlt'r asctnuU tVonj the iloepor l>inij ici^ions of llio mirtli into 
 " tho Volcano, wlicro it st-rvos I <>tli tor tlio lorniation ut volcanic 
 " ftsjj and of lav.'i. Ste/ini prodigicusly coniprc»Hod trioH, wlicro it 
 *' can, to break tliroii!j;li llio column of lava to the atmoh[)licrt». 
 "This escapo of stoani i.s thu principal causo of that subterranean 
 " noiso known as volcanic thunder. A continual struifoflo takca 
 "place betvvei'fi the elastic tlnid, tho fused rnasa and the solid 
 " walls of thu volcanic canal, which strugj^le lasts so lonu; as tho 
 " devclopniont of steam in tho latter contimies. I)uring this 
 "violent ascent of tho enormous steam bubbles, which buist on 
 " reaching the surface of the lava reservoir, pieces of lava alu mly 
 "cooled, or still fluid, are violently torn otf from tho latter and 
 *' thrown high up in the air out of tho crater. When the eruption 
 " is at its height, millions of these pieces, mostly red hoi, from tiio 
 " size of mere miscio^copio particles to those with a diameter of 
 " one or mure yards, till tho air abov(! thu crater, rising in myriads 
 "with each explosion, and falling again in per,H4u.illy changing 
 "motion. When tho intervals between each .vS|iln!,ioii are short, 
 " as is tho case with all violent eruptions, i; iiei|uently happe'-s, 
 ^ that during a lapse of about 20 seconds, whioh time tho glowing 
 " stones frequently take to complete their passage tiirough the air, 
 " six to ten new explosions take place. It is evidor.t that an uninter- 
 ' rupted volley and shower of stones mixed with the deiiso smoke of 
 ' finer particles will thus be sustained, and this it is, which, partly 
 "glowing itself, and partly lighted up by tho glow of tho melted lava, 
 "in the »;rater, resembles a permanent tlamo. Tho fragments of 
 "lava thus thrown out of the crater ditl'er from each other in size, 
 " in external form, (whitdi is frequently determined by the tcmpc- 
 "raturc at which thoy were formed,) and in ciiemical composition. 
 "Blocks have been observed measuring 4 to 5 metres each way, 
 " anialler ones about tho size of a cubic yard occur Irequently, 
 ''while from this sizo there aro innumerable gradations down to 
 "tho lineit dust. During an eruption, gravitation and tho force 
 " of the wind etTect a separation of the fragments according to tlieir 
 "sizes. The largest of them fall back into or close around tho 
 " crater, the small pieces are thrown further, while the finer par- 
 " tides are borno otf by tho wind and gradually deposited from it, 
 " the coarser particles first, and ultimately the finest du8t, which is 
 
38 
 
 ORIGIN OF ERUPTIVE AND rillMAIlY ROCKS. 
 
 *' often carried otY scvoral leanjiiC'* from the volcano. This fine 
 " dust is termed volcanic nsli, and furnishes tlie principal material 
 " for the formation of the layers of tiilf which arc so abundant in 
 '' volcanic districts. The fragments of lava possess at the moment 
 "of their ejection from the crater very different temperatures. 
 ■'Some of them, especially at the commencement of the eruption, 
 "are scarcely warm, an I possess tlicdaik colour of scoriae ; other?, 
 '* in greater quantity, arc red and white hot — the latter remain for 
 '* a short time fluid and perfectly plastic, form themselves into 
 •'rotating cH'p-oids, or fidopt ,soinetimp>^ abnormal long-drawn 
 "forms. Til se latter singular pieces hav>i been termed volcanic 
 *' bonibs. I'ccroasing in size, and becoming mixed with small 
 "angular figments, they graduate into what is called by 
 " the Italian , lai)illi, or volcanic sand." * 
 
 "When till' eruption has reached its climax, and the whole of 
 -.he crater to a certain level has beconie filled with lava, the latter 
 breaks out from beneath the dark crust tiiat generally overlies it, 
 at the lowest point of the bank of the crater, and rolls down the sides 
 of the volcano, forming what appears as a stream of fire by night, 
 and a thick viscid stream of slag by day. The lava leaves the 
 crater red hot, and as Ihiid as melted metal, but shortly afterward.s 
 the stream cools anil becomes solid on the surface, while it remains 
 for a long time fluid in the inside, the heat there hidden showinn' 
 :ts'.'lf here and there through the c 'arks in the solidified crust 
 As the stream robs on, these cracks close up, while others form at 
 'tthcr plac 's " Ttio whole surface is in continual motion ; at 
 *' one poii t -i-ge bubble-^ are olserved swelling up, which finally 
 " burst and .e:ivo their rugged siiles behind, standing erect in 
 " the most curious forms; at another point cakes of slag in the 
 " most varied positions are carried along, ploughing furrows as 
 ■' they go, or tearing half-lluid lava with them and drawing it out 
 '' and winding it round in curious rojie-like forms (the so called ropo 
 '' lava). At some points the surface folds itself into deep cylin- 
 " drical canals, which run on beside ea(di other and parallel with 
 '' ihedirectiou of the stream ; and at others, cross folds and depres- 
 " sions arc f>>rmed. Thus these lava streams present, in that part of 
 " their course where thi. strug^^lc between their fluid interior and 
 " the solidified crust has taken place, an extraordinarily wild and 
 " rugged appearance."! 
 
 
 h ; 
 
 * Dio vulcanidlie Gesleine iu Sicilien nud Island, p. 155. 
 ■■ Nauraann. Leiirbucli, I, IGl. 
 
ORIGIN OF EULTTIVE AND PRIMARY ROCKS. 
 
 39 
 
 According as a fused silicate cools more or loss flowly, tlie 
 structure of the resulting rock becomes more or less crystalline. 
 No lava shows on its suface distinct mineialogical cliaractcrs. 
 Although traces of felspar or augite cjystals make their appo ir- 
 ance sometimes, they are nevertheless ren lered unrecognizahle 
 by pieces of slag, the cavernous structure of the rock, atmospheric 
 influences, etc. The non-crystalline character of the lava crust is 
 of course attributable to its having been rr.pidly cooled. The great 
 stream of 1600 from Etna, which is often GO feet thick, is at several 
 places in the neighbourhood of Catania intersocteil by quarries, in 
 which the structure of its various parts may be studied. It is 
 only at the depth of several feet, that tlie lava begins to bo com- 
 pact and homogeneous. It here consists of a light gray felspa- 
 thic mass in which cry.-ials of black augite and grains of green 
 olivine are disseminatcl.* Many trachytic lavas of recent produc- 
 tion possess distinctly crystalline characters containing in the 
 compact mass crystals or grains of glassy felspar (sanidine). 
 
 From this sketch of various volcanic processes it would appear 
 that there are being formed at the present day rocks entirely an- 
 alogous to the basalts and trachytes, which have protruded them- 
 selves almo-t uninterruptedly through the earth's crust since the 
 commencement of the tertiary period. We observe them solidify- 
 ing from a condition as undoubtedly igneous as that of the slags 
 which flow from our furnaces, and we observe them generally as- 
 sumino- the form of streams radiating from volcanic craters, or as 
 layers on the more horizontal ground around these, which latter 
 f )rm uf deposition forcibly rtininds the observer of the basaltic lay- 
 ers of much earlier date and non-volcanio origin. Liva is not so 
 frequently observed in the form of veins as are the earlier tra- 
 chytes, ncveitheless it is sometimes observed in this form on the 
 sides of craters. Tlie earlier eruptions of tracliytic and basaltic 
 rocks seem to have taken place through tissurci in the earth's 
 crust, somewhat in the same manner as the older eruptive rocks- 
 The masses thus eruptdl assuuicd the ibrm of isolated dome shap- 
 ed hills or wiuc extended coverings, or even of whole stratified sys- 
 tems. In later peiiods we find ihesj rocks gtadually associating 
 themselves with volcanic openings, and occurring in the form of 
 lava streams, many of which are even traceable to the craters 
 which emitted them. Fissures seom to have become more diffi- 
 cult of formation in the crust of the earth and in their place those 
 
 * Yon Waltcrshausen : Gcsteine in Hicilien und Island, p. 100. 
 
■•WWiBIi 
 
 40 
 
 ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 canals of eruption seem to have l»oon developed, which tcrminato 
 on the surface of the earth in the craters of volcanoes. The tran- 
 sition from tlie earlier massive forms of deposition to tlie present pe- 
 culiar volcanic type is so gradual and evident, that it is impossible to 
 ascribe the former to any other cause than that from which the latter 
 has been derived. Moreover it is impossible to discover any 
 lithological dirtercnce between the trachytes of many lava streams^ 
 and other rocks of the same class, wliich occur constituting whole 
 mountain masses. 
 
 It is further a very remarkable circumsianoa connected with 
 basaltic intrusions that they have exerted upon the neighbouring 
 strata eflects which could only have been produced by great heat. 
 These cttVct'*, such as the rc-crystallization of limestone, the car- 
 bonizing of coal, etc., are too well known to require particularisa- 
 tion. Another fict which speaks for the igneous origin of basalts 
 is the following : — In many b.isaltic veins their sides or selvages 
 are composed of a crust of glass or slag, which gradually alters 
 towards the centre of the vein into the granular rock. This 
 circumstance is entirely analogous to that observed in many slags. 
 These are often quite vitreous on the surface, where they have 
 cooled (|uiid<ly, while beneath they assume a granular and even 
 crystalline texture. 
 
 In the first p;irt of ihis papm* I have referral to the chemical 
 composition of ceriain rocks of the tr.icliytic and basaltic grou is. 
 The analyses there giviMi were however of the extremely siliceous 
 trachytes and ba-^ic ba>*a!ts. In Bischof's Chemical and Physical 
 Geology there are recorded 27 analyses of trachytes, containino- 
 from 52 8 to 72-24 percent, of silica, and averaging 62-9 1 per 
 cent. In the same work there are given 22 analyses of dolerites 
 and basalts, the content of which in silica ranges from 32-5 to 
 o2-9G and averages 46-10 per cent. For the sake of completeness 
 I insert here a li>t of the various species of the trac.iyte and basalt 
 families, as given by Cotta, preparatory to adverting to certain pe- 
 culiarities in the structure of some of them, which peculiarities 
 will again bo referred to towards the close of the present chapter 
 in discussing the relation which exists betwixt granite and gneiss. 
 
 3fassive Trachjtlc Rocks. 
 
 Minornlogical constituents and priijcipal 
 characters. 
 Trachyte, Sanidin (glassy felspar) and albite 
 
 with hornblende or mica — granular. 
 * Gotta: Gesteiaelebre, p. 78. 
 
 
 
ORIGIN OF ERUniVE ANT PRIMAllY ROCKS. 
 
 41 
 
 Tracliytic porphyry, Impfvlpable baso witli crystals of sani- 
 
 fline, <kc. 
 Perlite, Elnaincl-liko mass; globular. 
 
 Obsidian and pumice stone, Vitreous mass ; impalpable to porous. 
 Phonolite, Impalpable schistose base. 
 
 A.ndcsile, Friable mixture of albite, oligoclase, 
 
 hornblondo and magnetic iron ore. 
 Tafaccous Tmchytlc EocJcs,^^ 
 
 Trachytic breccia. 
 Trachytic conglomerate. 
 Trachytic tuff. 
 Plionolitic conglomerate. 
 Pumice stone tuff. 
 Trass. 
 
 Pumice-stone boulders. 
 Pumice-stone sand. 
 
 « 
 
 Alumstone. 
 
 Massive Basaltic RocJcs.f 
 
 Mineral constituents and general characters. 
 
 Augite and lahradorite ; granular, 
 plia^nero-crystalline. 
 
 Augite and labradoritc ; constituents 
 crypto-crystalline. 
 
 Augite and labradorite ; impalpable, 
 crypto-crystalline. 
 
 Augite and nepheline ; granular to 
 impalpable. 
 
 Augite and leucite ; granular to impal- 
 pable. 
 
 Augite, labrador, analcime ; do. 
 
 Tnfaceous Basaltic Rocks-X 
 Basalt cono'lomerate. 
 Basalt lull". 
 Peperino. 
 Palaaonite tulF. 
 
 The rocks above mentioned belong to a class, the igneous 
 origin of which is regarded by geologists generally, as controvert- 
 
 • Naumann : Geognosio, p. 709. 
 
 t Cotta ; Gesteinleliro, p. 34. 
 
 t Naumann ; Geognosie, I. p. 712. 
 
 Dolerite, 
 
 Anamesite, 
 
 Basalt, 
 
 Nepheline-dolerite, 
 
 Leucite rock, 
 
 Analcimiti', 
 
ft-*«4^^^UWi 
 
 42 
 
 omaiN OF ERtrTIVE AND PRIMARY ROCKS. 
 
 jbly established. Novcrtlielesstlierc are to be found among ibem 
 instances of rocks possessing a chavaoterislic hitherto ahnost ex- 
 clusively ascribed to those of sedimentary origin. This is no other 
 than the arrangcnionl of some of the constituents of tlieso rocks 
 in a direction paraliel to certain planes or lines. There exist 
 numerous instances of undoubtedly igneous rocks possessing par- 
 allel structure as marked as that of many sedimentary rocks. 
 Many trachytic porphyries possess this, especially those from the 
 Island of Ponza and Falmarola, from the foot of the Oyamel in 
 Mexico, and from the mountain Pagns near Smyrna.* Hofl'mann 
 alsc describes a trachyte from the Island of Pantellaria, between 
 Sicily and Africa, which consists of a liglit greenish-grey compact 
 fundamental mas'*, with crystals of sanidine and another mineral, 
 which by their form, position and distribution occasion a marked 
 schistose structure. Tracliytes of this nature have been observed 
 in the Island of Basiluzzo between Stromboli and Lipari, and in the 
 Duchy of Nassau, f Slaty trachytes are also of frequent occur- 
 rence and have bcMi observed by Leopold von Buch at Angostura 
 and near Perexil in Tenerifle, and in the Canary Islands at the 
 Caldera of Tiraxana and at Mogan on Grancanaria. Also by 
 Burnt in Velay.cspeiially at St. Pierre Eynac,at the Pas-de-Compain 
 and in (he MontDore. J The slaty trachytes described by Burat are 
 classed by other geologists among the phonolites, which latter also 
 furnish most remarkable instances of parallel structure 'imong ig- 
 ncous rocks. Phonolites as a class possess this slaty structure, which 
 is caused i»y the parallel position of the tabular-looking crystals of 
 felspar contained in it, and on this account the rock can oi'len be split 
 up into slates and flags. Tills slaty structure suands also in connection 
 with the form ii\ which these rocks have been deposited. In phonolitic 
 mountains it is generally observed that the flags, and the layer-like 
 subdivisions of the rock correspontling to them are arranged 
 around the axis of the mountain in a bell shaped system of strata, 
 the inclination of tlie latter decreasing as the summit of the moun- 
 tain is api>roached. This winild seem to indicate that the parallel 
 structure was occasioned by the flow of the phonolitic material 
 from the opening in the summit over and down the sides of the 
 mountain. Thi;5 view is fiinher supported by the fact that many 
 lavas possess a marked linear parallel structure, sometimes com- 
 
 • LelirlKich, I, G32. 
 t Lelirbucli, I, G34. 
 i Lehrbuch, I, 635. 
 
ORIGIN OF ERUPTIVE AND PRDIARY ROCKS. 
 
 43 
 
 bined with an evident dist<'nsion of tlioir crystHllino constituents 
 in a direction parallel with the course of ilio lava stream. Accord- 
 ing toSpallanzaui and Doloniieu this phononicnon is of great ini- 
 portauco, ^incoit was doubtless occasioned by the moving forward 
 and the exu'iision of the half-lhiid lav;i, an ex[)lanation amply 
 confirmed \>v the elongation in the direction of the stream of tlio 
 cavities filled with gas which are oonlained in the lava. In the 
 Leucitedava d" liorghetto the crystal^ of Icncitc in ppite of their 
 tesscral form :iie even drawn out in the direction of the stream.* 
 These instances of parallel structure among tiic trachytic and bas- 
 altic rocks have been specially dwelt upon, because of the analogy 
 they present to gneiss and other scliisto^e rocks of the primitive 
 gneiss formation. 
 
 Porphyry, Greenstone, and Mehtphyr. — It has been already 
 mentioned, that the trachytic and basaltic rocks first make 
 their appearance about the couimencement of the tertiary 
 period. Instances of such rocks occur however even earlier, 
 in the trias formation, in passing ha-dcward through which 
 ■we find that their character gradually changes. Porphyries result 
 on the one hand, and melapliyrs, or commonly called traps, result 
 on the other. The rocks usually comprehended under tlie name 
 melaphyr are, according to Cotta, of a very indefinite character, 
 and resolvable partly into basalt, partly into greenstones, and 
 partly into por])hy rites (porphyries free from (piartz). On this 
 account it would appiiar advisable; to classify most of the eruptive 
 rocke, which have been protruded daring the Silurian, (^arbonifer 
 ous and Permian periods into two gn'at divisions, viz : porphyries 
 and greenstones. With regard to the igneous origin of these, I 
 cannot do hotter than quote the argument of Xaumann.f " We 
 " have seen, that if the rocks of the lava family (as no one di ubts) 
 " must be regarded as pyrogenous formations, then the rocks of 
 " the basalt and trachyte families have a similar origin. If now 
 *' the melapliyrs (or traps) are compared with the basalts, and 
 " the fclsitic porpliyrics with the trachytic [iorphyries, an aston- 
 " ishing similarity will ho observed t) exist between them; a 
 " similarity which renders it often quite impossible to distinguish 
 " the one from the other, when haiid-spejin)ens of them m(>rely 
 *' are examined. According to iHagmanu and l^elosse, we may 
 " recognize the same mineralogicid constituents in melaphyr as in 
 
 • Lelirbucli, I, 4G8. 
 t Lohrbucli, I, 737. 
 
sas!* 
 
 44 ORirilN OF ERUPTIVE AND TRTMARY ROCKg. 
 
 " ik)leiiie, aiiamosito, an I Uisalf. It shows ([iiito smilar atnyg- 
 •' daloidal tonus to tlicsf cf tho latter rocks. It is a massive 
 " rock, sometimes wiili coluniiiar tlovelopinent, n completely non- 
 " fossilitorous rock like basiilt. All thoso coiiiciileiices, from a 
 «' lillKjloi-'ical point of view alone, a{)pcar completely to justify the 
 " view that the m('hi[»hyis, hko the basalts, must be numbered 
 ** among pyrogenons ro.'ks. In the fclsite-porphyrics, it is true that 
 " common ortliucJasn takiis the place of tho glassy felspar of the 
 " tracljytes, still the tlilforenco between these two minerals must 
 "be looked upon as tri Hi ii^', especially when it is remembered, that 
 " most orthoclases contain somo soda besides the potash. More- 
 " over, the remaining const tuents, albit;^, oligoi'lase, mica, and 
 *• quartz are conun<>M to tho trachytic-|)orphyries and to tho 
 " andesitcs, as well as to the felsitic-porphvries, while the labra- 
 " dorite brings certain porpliyiites in very close relationship to tho 
 " melaphyrs, from which they are sometimes almost undislingiiish- 
 " able. The unprejudiced encjuirer will therefore surely without 
 "hesitation regard the felsitic porphyries as rocks ()uile analo- 
 " gons to the trachytic porjdiyries, with which they also 
 '' correspond in many other properties. Th-re are also other 
 " rocks, reoraniini; the orio-in of which we mu.-t come to similar 
 '' conclusions. The diabases con-ist, esscnlially of oligoclase or 
 " labradorite and pyroxene; the diorites of albite, hornblende, 
 " and (juartz ; both classes therefore i>f exactly the same minerals 
 " as we observe ociuirring in lavas, basalts and trachytes. In 
 *' niincralcgical and chemical re>[)ects therefore, no objection can 
 " be taken to the su|lpo^ilioll that they have been formed in a 
 " manner exactly similar to these latter rocks. When we add to 
 " this that these greenstone-; are always completely non-fossiliferous, 
 " generally massive and supplied with structures and forms of 
 '* deposition quite simibir to ihdse of the basalts and lavas, the 
 '* above supposition would ap[iear t > be in ev(;ry respect justifi- 
 " able." With regard to the clivmi(;al composition of these rocks 
 we find, that if \V(; take the analysis of thn c hi»rnblendic por- 
 phyries, and of a similar number of felsitic porjdiyries, ;is given 
 in B.schofT's Chemical and Physical Geology,the content^ of silica 
 of these ranges froiu 77.9 to o9.87, and averages 07.77 per 
 
 cent. If we further take the analvsis of oivcnsiones and mela- 
 phyres contained in the same work, we find their percentage of 
 silica to rane-e I'rom 55.29 tn 42.72, and avciam; 50.9. 
 
 Tlie pi)r|)liyries seem to have hcon formed principally during 
 the Carbonit'etous and Permian periods. They o'teii oc^nr in the 
 
ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 45 
 
 midst of i^raiiitos and Ryeiiites, in which tliey form veins, so that 
 they are generally newer than these latter rocks. A few of them 
 are decidedly older than the coal period, ami several have been 
 formed simiiltanoously wHli the Hundtsandstein of the Triassic, and 
 oven in the Jurassic and the challc formations, but the heiirht of 
 their development falls in tho irb )niforniis and the first part of 
 the Peniiian period, in the German Rothliegendos. In the latter 
 formation the por[)liyries have played a very important part, fur- 
 nishiniT the material for many of its sedimentary rocks, and dis- 
 locating its strata consid .'rably by their intrusion. In the carbo- 
 niferous system porphyries break through and materially disturb 
 the strata, forming veins or dykes, and inserting tliemselves hori- 
 zontally as layers. Whih', as we have already m-Mitioned, the 
 tasalis and trachytes exert a [towerfiil chemical action on the 
 rocks with whicli they come in c intact, the influence of the 
 porphyries seems to have been almost exclusively of a mechan- 
 ical nature. It seems as if the porphyritic material on its arrival 
 in the upper parts of the earth's cru-'t did not possess such a high 
 temperature or such a great degree of fluidity as the basalts. On 
 the other hand, the rocks broken tlirough by the porphyries, show 
 evidence of tlie enormous violence to whicli they have been sub- 
 jected, huge pieces having been broken off, surrounded by the por- 
 phyritic material, carried off by it, and crushed and pulverized in 
 its further progres-'. In this way have been formed the numer- 
 ous breccias which occur in veins and masses of porphyry, 
 where they adjoin the side rocks. Sometimes the mechanical 
 action has been so violent as to produce even a more finely di- 
 vided material, wliicli in the form of a sandstonedike or clay-like 
 substance constitutes the selvages of many porphyritic veins. By 
 far the most conclusive proofs however of the enormous forces 
 which were at work during the eruption of the porphyry, are 
 to be fuund in the dislosiations which whole systems of strata 
 have undoi'gone. The neighbouring beds have been raised 
 up, folded and fractured, while friction-grooves, and surfaces worn 
 smooth by the sliding of one mass upon another occur at the junc- 
 tion of the erupted rock with tlie neighbouring strata. These effects 
 furnish almost as conclusive evidence of the igneous origin of the 
 porphyries as the chemical changes on the adjacent rocks do, as to 
 the icfueous orijrin of basalt. 
 
 V/ith regard to the greenstones, they seem to have made their 
 appearance in very great profusion during the Silurian and Devon- 
 
46 
 
 ORiaiN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 ian periods, and even earlier, although in lessor quantity among 
 the primitive slates. In the Ciubonitbrous system, they are in- 
 truded almost as frequently as the porphyries ; but towards the 
 coranionceraont of the Permian period, they seem to bo replaced 
 by melaphyrcs, which continue to be erupted even as late as the 
 Triassio period. The circumstances attending the protrusion of 
 the greenstones and melaphyres are essentially the same as in the 
 case of the porphyries. The strata which the former have broken 
 through furnish aoundantevidonce of the extraordinary force which 
 ejected them, and the dislocated strata also occasionally furnish 
 proofs that they have been chemically acted on by the plutonicrock. 
 This latter is especially the case with the melaphyres, which have fre- 
 quently cirbonizc 1 the coal and hardened the clay slates with 
 which they have come in contact, in the same manner as more 
 recent eruptive rocks. In tlie following tables will be found the 
 names and characters of the rocks referred to in this paragraph. 
 
 Massive rocks of the Por^ihyry class,* 
 
 NAME. 
 
 Quartz porphyry. 
 Syenitic porphyry. 
 
 CRYSTALS OCCURRINO 
 IN THE PASTE. 
 
 Quartz and Feldspar. 
 
 CHARACTER OP TOE PAST.'!. 
 
 Granitic porphyry. 
 Micaceous porphyry. 
 Minette. 
 
 Yellow, brown and red 
 colored. 
 Quartz, Culorite f Brown or green ; 
 
 Feldspar, sometimes -j aomewhat granular. 
 
 Mica. [ 
 
 Quartz, Mica,Feld3par. Sometimes granular. 
 Mica and Felspar. Brown coloured. 
 
 Mica and Felspar. 
 Hornblendic porphyry. Hornblende & Feldspar. Dark coloured. 
 Felspathic porphyry. Feldspar. 
 Felsite rock. Sometimes Quartz. Yellowish, reddish, 
 
 or greenish-grey. 
 Pitchstone,and Pitch- 1 Glassy Feldspar, Qu.irtz 
 stone porphyry. J and balls of Felsite. 
 
 liocJcs made ujy of Porpliyrltlc dchris.f 
 Porphyry breccia. 
 Porphyry conglomerate. 
 Porphyry sandstone (psammite.) 
 Porphyritic tuff or felsite tuff. Claystone. 
 
 Massive rocJcs of the Greenstone and Melaphjre class.\ 
 
 NAME. ESSENTIAL CONSTITUENTS. TEXTURE. 
 
 Diabase. / ugite, Labradorite, and Granular, porphyritic 
 
 Oligoclase. and slaty. 
 
 • Cotta, Gesteinslehre, p. 97. 
 t Naumann, Lehrbuch, I, 706. 
 X Cotta, Gesteinslehre, p. 47. 
 
ORiaiN or ERUPTIVE AND rilDURY ROCKS. 47 
 
 
 tic 
 
 •NAME, 
 
 Crtlcarcous Diabase. 
 
 Gabbro. 
 
 Hypersthenitc. 
 
 Augite-rock. 
 Norite. 
 
 Diorite. 
 Globular Diorite. 
 
 Micaceous do. 
 
 Hornblende rock. 
 Hornblonde-slate, 
 Actinolite slate. 
 Kersanton. 
 Eclogite. 
 Disthenc rock. 
 
 Apbanite. 
 Serpentine, 
 Scbiller rock. 
 Garnet rock. 
 Eulysite. 
 Epidosite. 
 Labrador rock 
 
 KHHENTIAI, CONflTtTrF.NTS. THXTmE 
 
 5 Augitc,Labradoriteor i Granular, impalpable. 
 I Oligoclaao & Oulcito. { ' ' « . 
 
 Diallago or Sn 
 
 slaty, concretionary, 
 and 
 
 ,., ... . "l^") Granular, slaty 
 dito with Liiorado- > '' 
 
 rite and Saussiirite. 5 concretionary. 
 
 TTypcrstheno and Granular. 
 
 Labradorito. 
 
 Augite. Granular to impalpable. 
 
 f Hornblende and Felds- ] 
 
 ■j par, Ilyperstheueand }■ Granular. 
 
 ( Feldspar, J 
 
 Hornblende and Albite, Granular, slaty. 
 
 Hornblende and Granular and globular, 
 
 Anorthite. 
 
 ( Hornblende, Oligoclase.n i 
 \ Orthoclase and Mica. ^^'•"""lar. 
 
 Hornblende. Granular or impalpable. 
 
 Hornblende. Slaty. 
 
 Actinolite. Slaty. 
 
 Hornblende and Mica. Granular. 
 Sraaragdito and Garnet. Granular, slaty. 
 Disthenc -Nvith Garnet Granular, slaty. 
 
 and Mica. 
 Feldspar and Pyroxene C I^P^lpable, porphyri. 
 
 or Amphibole. ] ^^•=' '^''^^> ''^^''^^'' 
 
 ( .amygdaloidal. 
 
 Serpentine. 
 
 porphyri- 
 
 Impalpable, 
 tic slaty. 
 Schillerspar and .Ser- Granular, 
 
 pentino. 
 Garnet, Hornblende, ) 
 and Magnetite. \ Granular. ' ■ ' 
 
 Garnet, Pyroxene, Granular, impalpable. 
 
 and iron oxide. 
 Pistazi'e and Quartz. Granular, impalpable 
 
 concretionary, 
 Labradorite and Granular, porphyritic. 
 
 Hornblende. 
 
 Fragmeatari/ rocks of the Greenstone artd Mdaphyre class.^ 
 GrcenstDne concrloinerate and orreenstone breccia. 
 Greenstone sandstone (psamniiti'.) 
 Greenstone tuff. 
 Schalstone. 
 
 It will bi3 observed from llio foregoing tables, that by the 
 action of water on the porphyries and greenstones rocks have 
 
 • Naumann, Lehrbuch, I, 703. 
 

 48 
 
 OIViai» OF EUUl'TIVE AND rillMAllY llOCKS. 
 
 been formed .siniiliir to the coiigloiuiMiitcs fiml tulTs of the volca- 
 nic formiitions, ami probably in n similar m.iimer. Moroovi-r just 
 as in these formations we tind among the m.issivo rocks above 
 euumerated many instances of undoubtedly igneous rocks pos- 
 sessing a slaty structure. Many feldsitic porphyries possess a streak- 
 ed texture caused sometimes by bands of varying colour, and 
 oftencr by the arrangement of the nwwl/. grains or crystals in 
 narallel layers, or the presence of thin lamiiKC of (juartz in 
 ilie paste. -f^ The instances of a similar mo lilicanon of stru(;turc 
 among the greenstones are very mmierous, and they arc even 
 more important as showing more clearly the cause of this struc- 
 ture among igneous roi'ks. The diorites usually occur in the 
 form of veins, irregular masses (typhonischc Stiicke,) and layers. 
 The veins sometimes exhibit the following remarkable plienomena. 
 In the middle they consist of granular diorite, and at the sides of 
 slaty diorito or hornbl.nde slate, a gradual transition being gone- 
 rally observable from the granular to the stratified rock. Some- 
 what similar instances of this nature have already been referred 
 to in the paragraph concerning the basaltic rocks. The cause o 
 these phenomena may most reasonably be sought for in the circum- 
 stances attending the cojling of the rock, and they are most 
 likely the same as those which occasioned a similar structure 
 among the porphyries. The fluid rock of the diorite vein was 
 probably in motion in the centre, while the parts adjoining the 
 side walls were solidified. The current in the centre would have 
 a distending and arranging action at the junction of the fluid with 
 the solidified parts, and an elongation and parallel grou))iiig of the 
 minerals there being formed would bo the consequence. Not 
 only has this slaty texture been observed in coimection with veins, 
 but it has also been remarked, that the more irregular masses 
 of diorite assume a slaty structure towards their junciion with 
 tb« other rocks, the stratification being, as in the ca>-e of tho 
 veins, parallel with the line of such junction. Naumann adduoes 
 numerous instances of this sort ;f and from a former paper of 
 mine it will be observed, that they often occur in Norway.^ 
 Among the melaphyrs or traps the same circumstance is often 
 remarked. In the mehiphyr region south of the Hundsriick this 
 rock, when it occurs in veins, often possesses a degree of 
 parallel structure sufficient to cause it to separate into flags, which 
 
 • Lehrbuch, I, 616. 
 
 t Lehrbuch, II, 403. 
 
 t Canadian Naturalist, VII, 115. 
 
ORKJIN i>V EIUl'TIVE AND PRIMARY ROCKS. 
 
 40 
 
 lie parft'lc'l willi tho whIIh of tliH vein. Tho trap of Kerrera do- 
 cribod l»y Macciillo^h is aiiotlinr idstancu of sljity ttjxturo in trap 
 veins. In this case the ro>k eonslitnlinn; the Hides of tho vein is 
 till(!d with scales of niira, which all lie parallel to tho enclosing 
 wu'.lrt. Tho same author also roinaks coticornintj; tho liypersthenito 
 of Sky, that the crystals of hyperstlicnc •' are laminar and 
 " placed in a jio-^ition parallel tooach othtT, and iisin gneiss (otho 
 *• plane of tlio he<l in wliiidi tlioy lie." Another peculiarity, 
 which siicws till) intlucnce of igneous tlovv on the strucluro of a 
 rock is tho following : Tho aniygdaloidal varieties of melaphyr 
 sometimes pusses-* an arrangement of their cavities corresponding to 
 that possiisscd by the gjis, buhhles of lavas. They are often olon- 
 gated.in which case iheii longest axes lie pandlel to each other, and 
 wc may suppose as in the case of lava, to tho.lirection of tho flow 
 of tlio igneous material. 
 
 Gninilc and Si/cnitc. — Those formations inrludo thi* oldest 
 eruptive rocks, tlu; granites and gne'ss-granitos, whiidi dnrlnij;thc 
 primitive period seem to liave broken thiongh the comparatively 
 thin crust of the earth then existing. Later granitic eruptions 
 seem to have taken place with great fre(|ueney throughout the 
 Silurian, Devoniati and Carboniferous periods, after which they 
 gradually disajipoar. Syenite does not moimii to appear in the Primi- 
 tive Gneiss tormaiiou untd long after the lirst general dislocation of 
 the same and tho protrusion if tho granite had taken plaee. Tho 
 principal syonitic eruptions seem to liave ucurrcd during or shortly 
 after tho deposition of tho Silurian and Devonian rocks, although 
 there are many inst;uiees of much younger syenites. The rocks 
 appear after their protrusioti to have assumel all the forms of 
 occurrence, which wo are aceu>t )med to ob>orvo in plutonio and 
 even volcanic f))niitions ; irreguhir masses, covers, (nnppos), 
 layers and veins ; every form except the stream of tho volcanic 
 rock. But it is to bo remarked that instead of veins or dykes 
 being the most common form, as in the newer plutonic formations, 
 tho irregular masses jiropjnderate. These masses are not to ^'O 
 confounded with tho covers or cap rocks of the basalt and trachyte 
 formations. They are huge islands of granite as it wore, possessing 
 generally an elliptical shape, and occurring in the midst of stratified 
 rocks, which are sometimes vertical, and which often lean against 
 the granite as if it were the immediate cause of their inclined 
 position. One of tho most important phenomena observable with 
 regard to granite in all its forms of occurrence is the extent to 
 
50 
 
 ORIGIN OF EUUl'TIVE AND PRIMAUY ROCKS. 
 
 i; 
 
 U 
 
 wliicli it contains hujj;o innsst's mid PinnlK-r frnginents of other 
 roflvH. This is one of the piost concliisivo j)roof« of tho power of 
 tlio forces nt work diirinj^ tho protniHinti of tlio ;^ranitf', and taken 
 in conii'iition with its forms uf deposition fiirnislius incontrover- 
 tiblo eviilenco of its eniptivu orij^in. Ainonjj the objections which 
 have hetMi made to this view, the most important is lliat fonnded 
 on the circMiinstanco that the qnartz of graiute has hoen the hist 
 of its constitiiotits to solidify. Many theories have heen proposed 
 to account for this circuiiistance hnt it would ser/r necessary 
 before attoniptini;- ifs oxphuiation to ennuire whether Uiis aMeged 
 behavior of the quartz is really tlie fact. Ft is doubted by a few 
 geologists, and aUogetlior denied by Sartorius vonWaltorshausen, 
 who remarks that according to his experience in the primary 
 rocks especially in granite as well an in the volcanic rocks, cjuartss 
 corundum and periclaso have always first been separated. *' For 
 instance," he says, " I have minutely examined the granites from 
 •' Bav'.'i.o, from various districts of the (irimscl, from Mont Blanc, 
 " from the Okir valley (Ilarz), fi' mj the l>land of Mull and many 
 " other places, and those rocks show that the ipiartz solidified 
 "first, then the niiea anil finally Hie feldspar."-*^ Tn the face of 
 such a tlistiiiet statement it might not be safe to regard as 
 thoroughly established the fact whereon the above objection to the 
 eruptive origin of granite is founded. 
 
 With regard to the chemictal composition of granite, its content 
 in silica, according to IH analyses mentioned by 15ischof, ranges 
 from 03. 3 to 70.02 per cent., and averages 09.33 per cent. Only 
 two analyses of syenite are on record, the silica being estimated as 
 61.72 and 06.39 percent.; average 64,05. If w.- comparo these 
 figures with the average content in silica of other eruptive rocks 
 we finil generally a diminution in the f|uantity of silica as the rocks 
 become njore aii<l more recent, pr ivided always that their classi- 
 lioation into two trreat series of siliceous and more basic rocks is 
 kept in sihgt. Tfius the acid series comprehend: 
 
 Granites GO. 33 per cent, of silica. 
 Porphyries 07.77 " " 
 
 Trachytes 62.91 " » 
 
 The basic series on the other hand consist of : 
 
 Syenites 64,04 per cent, silica. 
 
 Greenstone and Melaphyrs 50.05 " " 
 Doleritea and Melaphyrs 40.10 " •' 
 
 • Die Vulcanische Gesteine, &c , p. 225. 
 
ORKJIN OF KRll'TIVK AND I'UIMAllV ROCKS. 
 
 51 
 
 IJutifion Hiitl Strori;; nio iiirliimd to txtoinl tlio tlioury of the 
 noriiml Iracliytic luul basiiltii; iii:i;j;iims, iiKMitiuii.Ml in tlio tir-t part 
 of this* paper, so as to iiuilujo tlio pliitonii- nuks, aiul to mainlain 
 that gratihcH, porpliyiies aixl tlio oKlor oniptivo rocks aro capable 
 of being aim) Pfganlod as inixiiiros of tlio two livpotlictical nieltcMl 
 niasrtos. Of coiirsu the saiuj objections wliicli apply to this 
 theory ho far as basaltic a:ul trachytic, rocks are coiicerneil, apply 
 also in the case of the oUlcr rocks. On the other hiinl voii 
 WaltershaiiHftrs theory, also previously ilescribeJ, furnishes a 
 complete exjilanation of the cause of the more siJiooons character 
 of tho older i^cks. The satno increase of density aiul of basic 
 COnstituentH, which ho supposes now to take place from thosurfaoo 
 to the centre of the earth, existed in the oldest gooNx^ical pcrioiis. 
 The fused material, which, on broakini; throuirli the earth's cti^t 
 soliditied to granite, was the uppermost concenlrio layer then 
 existing. It was lightest in weight and richest in silica. 
 Beneath it lay successive layerw graduating iuto each other, and 
 with the depth increasing in density and basic constituents. But 
 according to this theory, the magmas from which granites, porphy- 
 ries, and trachytes resultel ought to have had a position nearer 
 tho surface than the fused matter which on its eruption yielded 
 syenites, greenstones, melaphyres, and basalts. Jlcncetlie former 
 rocks ought to have been the first to (ipi-ear upon the earth's sur- 
 face. Porphyries ought to havtj preceded syenites, and trachytes 
 ought to have brokon ihrofjgli the earth's crust and solidified 
 prior not only to basalt but to greenstone and melaphyre. This 
 is, however, not the civ^o, awtl S.irtorius von WaUershauson fully 
 appreciates tho difficulty, irontioning that the tracdiyte of I'lsia 
 near Reikjavik, " which according to its miixiralogical ciiaracter 
 ' belongs to a higher lying zone nevertheless intersects in the 
 • form of a veui the strata of Iclandie traji, which in ir-ueral 
 " originate I'r un deeper regions."* To ex|diiin the difficulty he 
 resorts to the theory "that the earth's crust possesses ''ifferent 
 " thicknesses in difTereiit places, or that the surface of separation 
 " between the already so!idilied and the t-till tlui(' masses represent, 
 " a relief turned inwards, of mountains and valleys. Now where 
 " such a mountain accidentally reacdies down into greater depths, 
 " melted masses might be able, through tissures in it, prematurely, 
 " to escape to the surface, which masses might be broken through 
 " later by rocks of higher zones which had remained longer fluid.. 
 
 • Die VulkaniscliO Gesteine, etc. p. 337. 
 
52 
 
 ORIGIN OF ERUrXIVE AND miMARY ROCKS. 
 
 •' ■■• 
 
 
 *' The anomalies in the Esia trachyte formation might perhaps 
 " also be explained by movements of the fluid matter in the 
 " interior, or by alterations in the relief forms of tlie surface of 
 " separation just mentioned." The method of explaining these 
 anomalier. by movonients in the fluid matter existing beneath the 
 crust would appear to be the most reasonable, and I shall endea- 
 vour as briefly as possible to refer to it more minutely. 
 
 We have already seen in referring to the cause of earthquakes 
 and volcanic eruptions, that it is ncjt impossible that movements 
 take place in the interior of tlic earth similar to tides in the ocean 
 on its surface. We shall siipp.'se the two lines within the dark 
 coloured crust in the subjoined figure (1) to represent respectively 
 
 Fig. 1. 
 the normal limits towards the interior of the acid, and the more 
 basic melted matter, which in the earliest periods as now, may be 
 supposed to have graduated into each other and yielded all the 
 varieties of eruptive rocks now visible on tlie surface. We shall 
 
 llh 
 
ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 53 
 
 suppose fiirtlicr thai a cliangc comparatively slight takes place in 
 the position of the metallic ceiitro. It is evident that the conse- 
 quence of this would he to press (he higher zone against the 
 solidified crust, and further to each side, bringing the lower zone 
 in contact with the crust at «, as shown in figure 2. If at this 
 
 Fig. 2. 
 part of the crust there existed fisamcs or volcanoes, the denser 
 and more basic 7ii(tss, h wouid he erupted, vvhii« the acid 
 mass, c would n^niain in the interior. As soon, liosv- 
 ever, as the Ci.',ntral mass resumed its normal position the condi- 
 tions would he re-established fur the protrusion of the more acid 
 rock of the superior zo!.(>. In this way the alternate eruptions of 
 highly silicificd matter anil then of extremely basic rock with all 
 the innumerable gradations that exist, between them, would seem 
 to be capable of explanation. The amount of divergence of the 
 metallic mass from the centre neeessary to produce the etfect 
 
54 
 
 ORIGIN OF EHUPTIVE AND PRIMARY ROCKS. 
 
 ill) )ve described is so inconsit.lerablo, that it does not appear un- 
 reasonable to attribute to the heavenly bodies tlie power of 
 causiiKT it. Still it would bo ver\' <lesirablc if niatliematicians 
 won! 1 devote some attention to the subjec-t. 
 
 The rocks of the granite family have been arranged by Cotta* 
 accordinfjj to- their granular and slaty varieties, as follows: 
 
 ESSENTIAL CONSTITUENTS. 
 
 Feldspar and Hornblende. 
 Feldspar, Quartz, Mica aud ) 
 ilornblende. i 
 
 Feldspar, Quartz and Mica. 
 Feldspar, Quartz and Talc. 
 Feldspivr, Quartz and Chlorite 
 
 IlESULTINQ ROCKS. 
 GRANULAR. SLATY. 
 
 Syenite. 
 Granitic Syenite. 
 
 Slaty Syenite. 
 
 Syenitic Gneiss. 
 
 Gneiss. 
 Protogine Gneiss. 
 
 Granite. 
 
 Protogine. 
 
 Chloritic Granite. Chlor'tic Gneiss. 
 Feldspar, Quartz aud Graphite. Graphitic Granite. Graphitic Gneiss. 
 Feldspar, Quartz and Iron Mica. Iron Granite. Iron Gneiss. 
 
 Feldspar, Dichroite and Mica. Dichroite Granite. Dichroite Gneiss. 
 
 Dicbroite, Mica and Garnet. 
 Feldspar, Elajolite and Mica. 
 Feldspar, Quartz and Schorl. 
 Quartz, Schorl and Topaz. 
 Oligoclase and Mica. 
 Feldspar and Quartz. 
 Quartz and Mica. 
 
 Dichroite Rock. 
 
 Miascite. 
 
 Schorl Granite. 
 
 Topaz rock. 
 
 Kersantite. 
 
 Granulite. 
 
 Greisen. 
 
 not known. 
 
 Kersantite. 
 Granulite. 
 Mica slate. 
 
 ii'i 
 
 The sedimentary rocks of the granite family are as follows :f 
 
 Granitic conglomerate. 
 
 Syenitic do. 
 
 Gneiss brecci:! and gneiss conglomerate. 
 
 Arkose (Feltl=i.alhic sandstone). 
 
 These latter rocks, however, bear but little analogy to the 
 tufaceous rocks of later eruptive f^i-mations. Instead of being 
 formed and deposited simultaneously with their corresponding 
 massive rocks, they have generally beonderi veil from the abrasion 
 of these, loni^ after their eruption and solidification, and deposited 
 with the rocks of comparatively recent sedimentary formations. 
 There do not seem to exist or have been formed witli granitic erup- 
 tions any rocks of a tufaceous character. The obvious inference 
 to bo drawn from this circumstance is, that during at least the 
 older granitic eruptions no water or ocean existed on the earth, 
 
 • Gestein slehre, p. 114. 
 t Lehrbuch, I, 702. 
 
ORIGIN OF ERUPTIVE AND I'RIMAR^ ROCKS. 
 
 55 
 
 the 
 
 S 
 
 ing 
 
 si on 
 itcd 
 
 ions. 
 
 •up- 
 
 snce 
 
 the 
 
 irtli, 
 
 from the confiict of whiuh with the fiuid unvnito snch rooks coukl 
 result. At the time of these eruptions, therefore, the tenipeiatuio 
 of the earth's surface must have huon higher than the boihiig point 
 of wato", and the whole of the latter now cuudeiisod on the surface 
 mustthca havu existed only in the atmosphere. 
 
 With regard to the stratifierl varieties of granitic rocks it will 
 1)0 seen from tlie above table, that su.;h have been abundantly 
 developed. Even syenites occasionally possess parallel structure, as 
 is the case of those of the Plauensche Orund near Drcsden,of Ullern- 
 Aasen, near Chri4iania, and of tlie dlcnwald. A banded struc- 
 turc has been observed in the syenites of r>rottcrode in Thurin- 
 gia, of Jurgojaskaja in Asiatic Russia, and of the Malvern Hills. 
 Phillips regards this structure, in the latter instance, as having 
 been produced during tlu^ original solidilicaiiou of the rock.* He 
 remarks that " the laminar and banded structures may be regarded 
 as indications of erystalliz itiou under restraint, such restraint hav- 
 ing reference to particular planers in cousequonco of the pressure 
 of preconsoli ■,. -sd '^arts adjacent." One of the most important tran- 
 sitions observt ■ Jong these rocks, however, is the stratification 
 of granite, wlun-y ii gradually assumes the character of gneiss. 
 The most abundant and striking e.\ami)k's of this are to be found 
 in the Primitive Gi.Mss formation, where granite occurs in beds 
 between gneiss strata, and forms gradual but distinct transitions 
 into these, by the lamiiiie of mica gradually arranging themselves 
 parallel to each other, and parallel to the direction of the strata 
 generally. But tlie irregular masses of granite to which we have 
 already referred have also often been observed to assume a slaty 
 structure as tliey approach the rocks adjoining them. One of the 
 most remarkable exam[>les of this occurs in the Primitive Slate 
 formation of Upper Tellemarken in Xorway,cspeeially in the neigh- 
 bourhood of Aamdal, Vraadal, llvideseid, &.;. In the interior parts 
 of the granitic [trotrunion, the rock is thoroughly crystalline. 
 Towards its limits, gneissoid granite is developc<l, the folia'Jon ot 
 which is invariably paralL'l with the line of its junction with 
 the adjoining rock-. That the rook here referred to is decidedly 
 eruptive is proved by the numerous fragm.^nt'' of neighbouring 
 slate enclosed in it.f Instances of exactly the same jthenomenon 
 have been observed near Taubenheim, in Saxony, and in the valley 
 of the Schwarza, in Thuringia. At tlie latter pl ace the granite i s 
 
 ♦ Mem. of the Geol. Survey of Great Britain, II. 1, p. M. 
 + ^*h\l : Om Thelemarkcns Geologic, p. 7. 
 
56 
 
 ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 iu the form of a loiiij drawn mass, in tlie centre of whicli it is dis- 
 tinct and cliaracteristic, while towards tlic han<^'ing wall it gra- 
 duates into gnoi>8oid rook. The central granite or protogineof the 
 Al[)s, according to Delosse, also graduates at its limits into gneiss, 
 and this, according to Raymond andCharpcitier, is the case with 
 the colossal granite masses of the Pyrenees. These various in- 
 stances furnisli good grou; for maintaining that gneiss bears 
 the same relation to granite, that diorite slate or hornMende 
 slate bears to many granular diorites, the micaceous selvage of 
 the Kerrera trap vein to its granuhvr centre, and the num tous 
 instances of stratified or banded porphyrit'S or trachytes, to the 
 corresponding granular rocks. In short there would ap[)ear to be 
 reason for assuming that gneiss is as mucli an [j^neous rock, as 
 are the banded or stratified varieties of igneous rocks just men- 
 tioned. The instances just given prove at least that certain 
 gneisses are eruptive, because they are nothing else than an out- 
 ward covering, a cont ict mollification of tlie eruptive granitic 
 masses. There are, moreover, instances on record of gneisses occur- 
 ring in veins, and sometimes enclosing fragments of other rocks. 
 Humboldt mentions an instance occurring near Antimano, in Vene- 
 zuela, where mica slate is intersected by veins from thirty-six to 
 forty-eight feet thick, and consisting of gneiss filled with large 
 crystals of fcldsp.ir; and Fouruct maintains that in the mountains 
 of Izeron, true eruptive gneisses occur in veins intersecting otlicr 
 gneissoid rocks.* Darwin relates that the granitoid gneiss of 
 Balii:'. "ontains an 'ular fraijinents of a liornbK'ide rock, and tha' 
 a similai i^neiss o'ciirrin;ij in Butofoov) Hav. near liio Janeiro, con- 
 tains an angular jiieco seven yards Img ;ni I two broad, of a very 
 micaceous gneiss. f Instances of the same nature have been ob- 
 served by Nauru'inii n'\ar Ullonsvang in Norway and by Boeth- 
 lingk near Ilelsingfors in Fiidaud.^. The most satisfactory ex- 
 planation which can be given of the t'onnation of the gneissoid 
 selvage to granitic masses is that which is given by Phillips in 
 the case of syenite, and already fpiolod. It is a consecjnence of 
 crystallization under restraint or pressure, accompanied by a 
 movement of the solidifying mass somewhat in the same manner 
 as indicated in the case of greenstone. Naumann adopts almost 
 the same explanation in referring to the formation of igneous 
 
 • Naumfinn, Lehrbuch, 11, 180. 
 
 t Geological Observations on South America, p. 141. 
 
 \ Lchrbucli, II, 113. 
 
ORIGIN OF ERUPTIVB AND PRIMARY ROCKS. 
 
 57 
 
 •tiata. His remarks on this point are as follows : " Let us imagine 
 that an igneous mass cryetallizing as it slowly cools, is confined 
 between two parallel planes, which exert both pressure and re- 
 sistance ; the cooling, and consequently the solidification will com- 
 mence at and proceed from these enclosing olaues. Now, if in 
 the solidifying mass the conditions exist for the development of 
 many lamellar bodies (r.uoh as crystals of mica) then each of 
 those bodies will, in consequence of the pre.^sure, assume a pooition 
 paraildl with the enclosing surface, and the rock will be furnished 
 with a plane parallel structure more or less distinct If, further, 
 ihe pr >ce83 of solidification does not progress regularly, but with 
 periodit' 'nterruptions, then the ro,-k would be divided into layers 
 lying parallel to tlie enclosing i>Uines. If the whol^ mass, during 
 the progress of the solidification was in regular motion up and down 
 then there would be developed in eacih a linear parallel structure 
 or distension of the rock more or less distinct." * Whether the 
 parallel structure of the gneiss of the Primitive formation maybe 
 attributed to causes similar to those here indi^;ateu, is a question 
 reserved for consideration in the third part of this paoer. Mean- 
 while it may bo remarked that tlie granite occurring in beds in 
 that formation, between the zones or layers of gneiss is so intimatey, 
 connected with tlie latter rock by lithological transitions that it 
 would seem to be altogether inseparable from it, and that the 
 same origin attributed to the one must belong to the other. In 
 the gnei:?s-granit,e of the mountains of Lower Silesia, the granular 
 and slaty modifications of that rock are, according to Von Eaumer. 
 regularly intjrstratiiied with each other. In Podolia, according 
 to Von BliiJe, granite and gneiss together form a whole, to which 
 a contemporaneous and similar mode of formation is ascribable. 
 In Scandinavia and Fin'and, in the central plateau of France, in 
 Scotland, in Brazil, and Hungary the same relations betwixt granite 
 and gneiss exist. *' En IIongrie,"t says Beudant, "ces deux roches 
 se raontrent toujours ensemble et nniqueraent ensemble, elles ne 
 forment pas des couches alternatives, mais uno seule et meme 
 masse." If, therefore, granite, as we have seen, is undoubtedly 
 igneous, then the primary gneiss must be of the same oiigin, and 
 in this manner we obtain a proof of the original state of the 
 igneous iiuidity of our globe. Gneiss is the oldest formation, and 
 if it can be reasonably shown to be igneous, then it must have 
 
 Lehrbuch, I, 496. 
 
 Voyage en Hongrie, IH, p. 19. 
 
 
 B 
 
68 
 
 BELL ON THE VALUE OP 
 
 ,^^v 
 
 I 
 
 been the rock first solidified ; and previous to this, it, as well as all 
 subsequent eruptive formations, and the material of all sedimentary 
 rocks must have been in a stiUe of igneous fusion. The theory of 
 the igneous state of the original globe is, however, probably so 
 well established as to require no further proof. It is an axiom 
 without which it is impossible satisfactorily to account for the phe- 
 nomena of volcanoes and hot '^-ings, the elevation of mountains, 
 the increase of temperature oi. netraling into the earth, the phe- 
 nomena of terrestrial magne*, im, the formation of crystalline 
 rocks, and the flattening of the earth at the poles. In the third 
 and concluding part of this paper I shall advert more fully to this 
 hypothesis, of the conditions which must have co-existed with the 
 earth's original fluid state. 
 
 III. The Primary Formation. 
 
 Following out the plan indicate^' in the first part of this paper, 
 we proceed to the consideration of the primary rocks, with the 
 viaw[of ascertaining whether they, in part at least, may reasonably 
 be regarded as constituting the first solidified crust of the earth 
 The igneous condition of the original globe has already been ad- 
 verted to, and it would seem unnecessary here to refer at length to 
 what may be called the keystone of this theory, viz. the flattening 
 of the earth at the poles. It is suflicient to remark on this point, 
 that Newton and Huygens first maintained and proved this to be the 
 case, from mathematical grounds alone. Subsequently numerous 
 measurements of the length of a degree in various lands, but es- 
 pecially in those near the equator and under the polar circle, have 
 thoroughly established the truth of Newton's theory. They have 
 proved that the length of a degree of latitude increases with the 
 distance from the equator. The following are some of the results 
 obtained : 
 
 Peru 
 
 India 
 
 France 
 
 Eripiand 
 
 Lapland 
 
 The meridian lines are therefore more considerably curved in 
 the neighbourhood of the equator than at the poles, and the 
 equatorial diameter of the earth is consequently greater by about 
 24 geographical miles than the polar diameter; This is of course, a 
 
 • MuUer's Kosmische Physik, p. 51. 
 
 Latitude. 
 
 Length of degree of 
 Latitude. 
 
 l^Sl 
 
 56736.8 toises. 
 
 12032 
 
 56762.3 « 
 
 4608 
 
 57024.6 " 
 
 52°2 
 
 57066.1 " 
 
 62O20 
 
 57196.2 " • 
 
ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 
 
 69 
 
 be of 
 
 led in 
 the 
 kbout 
 
 rse, R 
 
 consequence of the revolution of the earth on its axis, and of the 
 influence of centrifugal force. This influence could not, however, 
 have madrt itself felt, had not the earth been originally in a fluid, 
 or at least plastic condition, so that the depression at the poles 
 constitutes one of the most uuequivoc^ proofs of the original 
 fluid condition of the globe. 
 
 Assuming this fluid condition to have ber^n owing to the pre- 
 valence of an extremely high temperature, we are necessitated to 
 suppose that the atmosp' are was then very diff'erently constituted 
 than it is at preset. \ This has been remarked by many previous 
 writers. T>r. Hunt describes it as "an atmosplicre hoLling in the 
 state of acid gases all the carbon, the sulphur and the 
 chlorine, besides the elements of air and water."* Quensted re- 
 marks : " According to the igneous theory the whole of the sili- 
 ceous rocks were originally in lava-like fusion. It follows of 
 Course that not only the whole of the sea must have existed in the 
 atmosphere, but also a multitude of substances, which could not 
 exist otherwise than in the gaseous state, such as carbonic acid, 
 chlorine, sulphur, etc."f These inferences are l"^-^ "mately drawn. 
 The sandstones, shales, and the fixed parts of the nmestouci of sedi- 
 mentary formations then existed in the fused matter, along with 
 the materials of the igneous and primary rocks, the soda of sea- 
 suit and the inorganic constituents of plants and animsils. On the 
 other hand, the carbonic acid of the limestones must have existed 
 in the atmosphere. The chlorine of the sea salt also could scarcely 
 have existed anywhere else than in the atmosphere in combination 
 with hydrogen, or with those metals which form with it volatile 
 chlorides, such as lead, zinc, copper, iron, cobalt, nickel, 
 etc. Those volatile chlorides, which are decomposable while 
 in the gaseous state by oxygen, (such as those of the three 
 metals last named) c^uld not however have existed in an atmos- 
 phere containing free oxygen, but it would seem, that the 
 primitive atmosphere did not oomain any such free oxygen. 
 Bischof first adopted this view. He maintains that the carbon 
 disseminated through the dark clay slates of the pre-carboniferous 
 periods, is in itself more than sufficient to take up all the oxygen 
 which the atmosphere of the present day coutains.J He calcu- 
 lates also that a stratum of carbon, spread over the whole surface 
 of the globe, 2.6 feet thick, would be suflScient to convert all the 
 
 * Canadian Naturalist, p. 202. 
 
 t Epocbeu der Natur. p. 20. 
 
 t Chem. and Phys. Geologie, ii. p. 35. 
 
«0 
 
 OWalN OF fJRTTPTTTf; AND PRIMARY ROCKS. 
 
 N 
 
 !!?; 
 
 ■ 's 
 
 oxygen of the atmosphere into carbonic acid; and after consider- 
 ing how richly furnished the sea is with animal and vegetable life, 
 how rich its sedimentary deposits must be in organic eubstances; 
 that the earlier sedimentary rocks are highly changed with car- 
 bonaceous fiud bituminous substances, that betls of coal and 
 lignite are spread over an area of many hundreds of square 
 miles with a very considerable average thickness, he comes to 
 the conclusion, that a layer 2.6 feet thick is far from being an 
 equivalent to all the carbon existing in the earth, leaving 
 altogether out of the question the carbon of the organic world 
 on its surface. This opinion certainly seems to bo well grounded, 
 and tbere wouM appear to be just reason for supposing 
 that the oxygen of tln^ atmosphere existed original!} in the 
 state of carbonic acid, and that a considiM-ablo qnanli*^y of 
 carbon, besides thai wiiic-li was in combination with the oxygen, 
 must have existed in the original alinosphtTt', cithtir free, or in 
 combination with o'her elements, find probably especially with 
 hydrogen. Thus tiic gaseous iMivelope of th« original globe 
 must have been an cnonuons atinos])hL're of water, carbonic acid, 
 carburctted hyilrogen, and nitrogen, togoilier with comparatively 
 small (juantities of .sulphui'ons acid, and snIpliMreltcd hydrogen, 
 hydrochloric acid and metallio chlorides. The pressure of such an 
 atmosphere must have been prodigious, at least 100 times greater 
 than that of the present time ; and in conjunclion with itscorapo- 
 BJticn sufficient to produce effects totally dltfiTeiit from those 
 caused by atmospheric influences at the present ilay. Among its 
 most remarkable properties must have been its power of absorb- 
 ing heat. Dr. Hunt has shown that the atmosplicre of pa'eozoic 
 times must, from the amount of carl)onifi acid in it, have greatly 
 aided to produce the elevated temperature then existing.* 
 How much more must this have been the case when the atmos- 
 phere contained such hydro carbons as marsh and olefiant gases, 
 whose power of absorbing radiant heat greatly exceeds that of 
 carbonic acid.f Dr. Hunt has indeed indicated tliepart which such 
 hydrocarbons may thus have played. After the fluid globe had suflS- 
 ceotly cooled, to allow the condensation of some of the constituents of 
 this primitive atmosphere, the action of these on the earth's crust must 
 have been very energetic, and must have caused the formatiom 
 of products differing considerably from the sedimentary deposits of 
 
 • Canadian Naturalifit, vol. viii. p. 324. 
 t Tyadal : Heat considered as a modo of motion, p, 362. 
 
 
ORIUIN OF ERUPTIVE AND PIUMARY ROCKS. 
 
 Gl 
 
 ;mos- 
 ;ases, 
 lat of 
 
 such 
 jsuffi- 
 Intsof 
 
 must 
 latioa 
 
 sits of 
 
 later periods. We shall return to this subject, when adverting to 
 the rocks of the so-cuUod Primitivo Sl;ilo formation. 
 
 With regard to the tluid part of the original globe, we have 
 seen that it must havo been made up, with but little exception, of 
 the inorganic constituents of the earth's crust. It is evident, 
 that in tliia fluid globe the heavier particles must have found 
 their way to the centre, and that then, as now, the interior of the 
 globe must have had a greater density than its surface. Indeed, 
 the fact that this is the case at tlie present day is another proof that 
 the globe must have been originally in a state of igneous fluidity, 
 otherwise we could not aecount for the accumulation of the den- 
 ser particles at the centre. In the same way as the densest par- 
 ticles wereinflue.iced by gravitation, sr must also the fused sili- 
 cates of different densities, and the metallic sulphurets and arsen- 
 iurets have found their places in successive concentric zones, one 
 beneath the other, according to their increasing specitic gravities. 
 Thus the theory of Sartorius von Waltershauson would appear to 
 be as fully applicable when the earth was in a fluid state, as at 
 the present time. 
 
 There is nothinij unreasonable or inconsistent with the observa- 
 tions which we are able to make at the present day, in supposing 
 the inorganic constituents of the earth to have once been in a st^te 
 of igneous fusion. The various layers of fused material, to judge 
 from the rocks resulting from tlieir solidification, must have close- 
 resembled in chemical composition the scoriiu produced in differ- 
 ent blast-furnaces. If we suppose the uppermost highly silicified 
 and consequently most difiicultly fusible layer to bt; represented 
 by granite, we find many instances of slags from iron-t'urnacea 
 havinjj almost as acid a composition. Many granites contain only 
 C3 per cent, of silicM, but those of the Hartz as high as7n>0n the 
 other hand there are instances of uon-sl;igs containing 70 and 71 
 per cent.f silica. So far as the other more basic layers and the 
 rocks resulting from them are concerned, wc can find their equi- 
 valents among the slags of iron, copper and lead furnaces, since 
 the silica contents of ihe latLef range from 70 through every per- 
 centagedown to 8 p.c. If we coniinue the analogy, and suppose 
 the properties of these slags, to correspond somewhat to those of 
 ^he eruptive rock'o having a similar chemical composition, we 
 
 ♦ Bischof : Chemical aad Physical Geology, III. p. 414. 
 t Kerl : Handbucb der Huttenkunde, I. pi 323. 
 
62 
 
 ORIOIN OP ERUPTIVE AND PUIMARY ROCKS. 
 
 may find a cluo to the explaiuition of tlio various forms of 
 deposition, and other characterislics of the hUter. Thus it 
 18 well known thai the shigs in which silica preponderates flow 
 sluggishly and solidify slowly, while basic sings flow quick and 
 hot and harden suddenly. It may reasonably be concluded, that 
 the rocks of igneous origin would act similarly, and that conse- 
 quently granites, porphyries and trachytes would be more viscid* 
 and have better time for cooling and crystallizing, than the more 
 basic greiMistoues, Miolaphyres and basalts. The greater freijuency 
 of impalpable and finely granular varieties among the latter 
 rocks would be in this way accounted for. 
 
 We now proceed to consider what must have been tlie conse- 
 quence of the gradual radiation of heat from the igneous globe. 
 " I know of no mode," says McCulloch,* " in which th'i surface 
 of a fluid globe couM be consolidated but by radiation, while of 
 the necessity of such a process I need not again speak. The 
 immediate result of this must have becMi the formation of rocks 
 on that surface ; and if the interior fluid does now produce the 
 several unstratified rocks, the first that wore formed must have 
 resembled SL»mc of these, if not all. We may not unsafely infer 
 that they weregrinitic, perceiving that substances of this charac- 
 ter have been proJuiiod wherever the cooling appears to have 
 been most gradual. The first apparently solid globe was there- 
 fore a globe of granite, or of those rocks which bear the nearest 
 'crystalline analogies to it." To these utterances we must in the 
 main assent, inquirino; however whether the relations oxistinnr at 
 the time of this first solidification might not have given rise to 
 the formation of schistose granite or gneiss. Nothing is more 
 conclusively established, than that there exists, at the present day 
 in the atmosphere and ocean, a series of currents, caused by or 
 attributable to the <liiirnal motion of the earth. May not similar 
 currents have been in operation in the fluid igneous material, 
 during the first solidification of the earth's crust? Is it not pos- 
 sible that after this solidifi(;atioM had commenced, the outer shell 
 may have moveil quicker than the fluid interior, from oust to 
 west, and that the gradual accumulation of crystallized rock on the 
 interior of the crust may have taken place under circumstances 
 similar to those so well described by Naumann in referring to the 
 parallel structure of certain igneous rocks ? f There are not want- 
 
 • System of Geology, vol. ii. p. 417. 
 t Canftdiau Naturalist, vol. viii. p. 375. 
 
tlwn to obsorvo m ,l„g, ,•,,„„ "l';, ' . , ^''"""« ■» moro „„„„„J 
 b"-')".! »|.|>ca™„e„, evid„, t "l" "".T" ",•""''"'' ""■"'"'e.l or 
 ■»ot">niutli6i„,e,i,„.a,„l,,,.^, " ''*' ""■ ''i"'"-""' rate of 
 
 *s- T,,i, phc.„o,„„„:: t:-:,,;;^- ?'•"- ','™-« ...»::: : 
 
 ■■•on-worl,, Scotl„„J, „„d mo o ;;,;''?',?:', ,»' "■« %l".to„ 
 
 ' On 11,0 Olacior, of i,,e Ai„, .,'' " ^'"' \ 1>'"lal, i„ |,i, „rfc 
 
 pressure, „k, tl,„ fi,;„„ „. ;"".';"7;'" .°" »•■ "»x s„,,io«e<, 
 'ie motion under pro,,.,™ of/"' '""'■■'' "»"• «^« caused by 
 rtances. Not onlv h,» a banded, „ r""""""'« """" '"b 
 
 certain f„rna«scori,„, but ' 'f "™ ''""" '"-"«■' "™ong 
 
 I'ossea, so,netin,es both ,ib„, ' ^ :V7" '""" °''*'-^ '» 
 ^lag horn the " Pri,el,fcuer " ! .° " "':'"'""■'»• H'" «>. 
 ■narked fibrous texture, and si,,; J "','" ""■'"»- P-^^o^ a 
 P™U>.oed at t,„ bla,.'.f„r ae:\:'M,;V"""'"'""'^'-'-« - 
 formed s„i„,n,i„g on ,„,.,ted i.l„ i r''™,''^' ■'''"' '""«' » 
 t.iet wu), tl,e eold air. Snmil Ir , '"''"■•"' ™">«"' con- 
 fco of roolin,, slate, no. „ '" f' '" "'"« "'""''>" '>'« ™- 
 'Leireleavago. lu largerTiis „* fe';,"''''""-''"''"' ^"' »!» m 
 b'-ed witi, tte slaty one botlV •'•"'■"""''">"•"■» »'«'>n- 
 
 jrom these i-taucosfa,:;'::,- 1 ir :;:".? ""° ^-'' »"-■•* 
 
 lal currents at that period i, bill? "'"' """""'""C" "f inter- 
 not unreasonable to evp e , L '* ^ T'*"'""' " "<""'l "PPcar 
 "--.rfaeeofthefiui;;: o„ 7° "' "r. '"■'^^ ™"'"«cd'„n 
 ■mpo^siblo to suppose U,a, ; T°"'"''''"°^'^'"™cluro. It is 
 
 neath ti,o solidify" tui;;:;""''''^' ""■" '"»'-" " - 
 
 "ve position to tl latte" ;„ ! 1' ;;r ''7"" "" """" -'»" 
 globe. Tl,e liquid rook bone- a i,!'",'""'^' '"'"'"''o" "f 'be 
 one direction o; other almo^^K™'""'" ,""'» .-ved in 
 "'cr under the ice which co.4, i -n ,""'""■ "^ " '''o^e" 
 •niting from this soiidilie .ti„„ ," , ' ""°"' '*'™c'"re re- 
 
 rese,„bledmorethef„ t! r; ::'"°'"" '""^' '«"'-- bav„ 
 
 »tratilieatio„ofsedimet ;,.,:";■ ''T'"!: "''^ "■»» 'b. 
 and gneissoid rocks l,a I i'r' "'", ""'■"'fication „f g,,,,,. 
 
C4 
 
 ORIOTW OF IRTTPTTVR ANT) PRIMAHY ROCKS. 
 
 cation of t1i*»Ho ijjncourt r(>«;ks, may l)0 owiiij; to tlie principle which 
 occjwions tht<ir Utility." Co(jii:in<l rei^urdt pnoisn an ii "granite 
 »tratoi<le, maia non «tralirt6."* Kiviiire opines also that (jneiis 
 does not form true layers, but i» only a tineile or pseudo-Btrntiticd 
 rock.t Evon McCnlloch make* the following admission: 
 *' OneisH has not yet indeed pn'wjnlod any decided marks of that 
 raechanic.il arrangement whicli »o often occura in the other 
 stratified rocks; since 1 must explain tho paralUdism of the mica, 
 which has been supposed a prouf ot" such arrangements, in a very 
 ditferent way. In hyporsthene rock, an unstratilied member of 
 the trap family, the crystals of that mineral often occur in a 
 similar laminar manner, so aa to oommiinicale a fissile tendency 
 to it; and in Korrara mica ilh«>lf is thus found not only in a 
 mass of trap, but in a vein of the same substance, with the 
 same parallelism to the sides of the vein as it has to the plane of 
 the stratum in micaceous schist."^ The idea that gneiss may 
 have been formed in the manner above indicated is not entirely 
 new. In 1846 it was stated that tlie gneiss of the Saxon Krzgc- 
 birge *' perhaps difi'ers only from granite because it sohditied 
 under the influence of certain priissur'>s or tensions.|| 
 
 Whether the explanation here attempted of the parallel struc- 
 ture of gneiss may be regarded as ad»>quat'* or not, it does not at 
 any rate seem to be any more far-fetclied than Iho theory which 
 attributes this phenomenon to the influence of electfio magnetic 
 currents (Scheerer's theory) or even than that which regards gneiss 
 as a sedimentary rock, altereil in some obscure manner by heat 
 or other agencies. Hcsides the arguments given above in support 
 of the first mentioned view, there are also some general considera- 
 tions in favor of the existence of a primitive formation, which are 
 stated as follows by Naumann.§ "The oldest seilimentary forma- 
 tions must have had some material fiom which they could be 
 formed, and a foundation on which to be deposited. The whole 
 series of sedimentary formations must have been borne by some- 
 thing, and the material of at least the first member of this series 
 must have been derived from something, which something cannot 
 be assumed to be the result of a sedimentarv operation." 
 
 ♦ Bull, do la Soc. Geol. tomo ix. 1838, p. 222. 
 t Compte rendus, tome xxv. 1847, ]). 898. 
 i System of Geology, Vol. II. p. 152. 
 
 II Geogno3ti3che Beschrcibung des Koalgroiches Sachsen, 2te3neft, p. 
 122. 
 § Lehrbuch der Geognosie, ii., p. 8. 
 
ORIOIN OF KHUPl'IVR AND PRIMARY HOCKS. 
 
 65 
 
 " lu the name way thuro mimt biivc existed a oovoriiig lliroiigU 
 wImcIi tLe oldent Hruplivc fonuiitionH wore protruded, and u founda- 
 tion upon whiidi tlun could Hpread tiujimt'lves out; and tho whole 
 peries of cruptivo ro(;k» nmst, lii<o tlioHo of »«iliniet»tary origin, have 
 at the commencement been borne by soinethintf which cannot be 
 regarded »ih tho rusidi <»f hii cruptivo operation." 
 
 " We find ourtHjlves thus obliged, froui two sides, to assume the 
 existence oF an originally ovisling solid crunt of ihu planot, which 
 formed the theatre and lliu ftniniliitiou for all tho later fonuiitions 
 above and beneath which thoso two onorgicH in riatiiro ooidd de- 
 velop themaelves ; through which on the one siile the sedimentary, 
 and on tho other side the eruptivo formationH wen- brought into 
 existence ; and that formation of which ti»is original luundation con- 
 sisted it is con9e«pienlly proper to entitle the priuutive or theme- 
 liao, tho original or fundamtMital formation." 
 
 *• To this formation those enigmatical, <le»peHt-lying rocks belong 
 which resemble sedintieutary strata, in pos»<.'s-»ingmoro or less per- 
 fect stratitioation, and which resemble tu'uptivo rocks, when their 
 mineral composition and their crystalline structure are tak i, .:.to 
 consideration; but they are devoid of the fragmentary rocics and 
 tho organic remains by which the sedimentary formations are 
 ciiaracterized, and on the other hand do not possess the veins, 
 masses and streams common to eruptive rocks, nor the abnormal 
 relations of these at their junction with other rocks. In a word, 
 we meet in the primitive formation m;iny of those rocks which we 
 have al>ove designated cryptngenous, such as gneiss, mica schist) 
 hornblende-schist, etc. ; rocks whose unaltered cliaracter we are 
 not justifio'l iu denying in every case, merely because in some 
 cases similar rocks have been formed by th. rpotamorphosis of 
 sedimentary strata, or in an eruptive manner. T; ose who, because 
 a few beds of mica-schist or gneiss have been admitted to be meta- 
 morphosed clay-slate or greywacke slat':, declare that all mica- 
 schists and gneiss are ojily altered sediiiientary rocks, only meta- 
 mctamorphosed beds of mud, virtually remove the ground from 
 beneath our feet, and limit us to a transcendental suc<;essiou of 
 sedimentary deposits, which, "downward, has no end, or rather no 
 tlemonstrable commencement ; because finally the actual sediment- 
 ary origin can neither be recognized nor proved, but can only be 
 maintained as a hypothetical assiun[)tion." 
 
 "Tho primitive formation appears to possess quite an extraor- 
 dinary thickness ; and to reach very far down into the depths of the 
 
66 
 
 ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 m 
 
 ■i' 
 
 iff 
 
 S 7 
 
 .!"- 
 
 "X I 
 
 
 earth. At the same time it shows in a remarkable manner, in thoso 
 different regions where it comes to the surfaee, snch a general resem- 
 blance as regards its rocks, their structure and form of stratifica- 
 tion, that one is led from this alone to think that some stupendous 
 process must have taken place over the whole surface of the earth 
 at the same time and in the same manner, and that it is to this 
 process that the primitive formation owes its existence ; and even, 
 although it may be so completely covered over in regions of im- 
 measurable extent tUac in tliese it is not observed to come to the 
 surface, still we are enlitlcd with complete justice to suppose the 
 existence of an uninterrupted extension of the same, under all the 
 sedimentary and eruptive formations with which we are acquainted. 
 
 "The necessity of a primitive formation is besides so appa- 
 rent that one can scarcely comprehend how its existence could 
 ever be doubted. It appears, in fact, to be a first and indispensa- 
 ble condition, without which the possibility of sedimentary, as well 
 as of eruptive formations cannot be comprehended. The primitive 
 formation has also been, by different authors, entitled the prozoic* 
 azoic or hypozoic formation, ''ocause it existed long before the com- 
 mencement of the first races of animals or plants, and therefore 
 contains not a trace of organic remains, and lies beneath all fossili- 
 ferous formations. Bat all eruptive formations are likewise azoic; 
 the oldest sedimentary formation is likewise prozoic, and the term 
 hypozoic is perhaps a word which does not correspond suflSciently 
 well with the idea intended to be expressed by it." 
 
 "It is possible for us to regard the primitive formation perhaps, 
 as the uppermost part of the original solidified crust of our planet ; 
 and this supposition has here and there been adopted. We leave, 
 however, the process of their formation undecided, and rest satis- 
 fied, in the meantime, with the negative result, that according to 
 the present condition of our knowledge, the primitive formation 
 can neither be a sedimentary formation, in the usual sisnification 
 of the term, nor yet an eruptive formation, properly speaking. It 
 is however a most remarkable fact, that a few companitively 
 far younger form:itions show a surprising similarity to the primi- 
 tive formation in the structure and architecture of their rocks 
 (viz., the Munchberggneiss-formalion in Oberfranken, and the pro- 
 togine formation of the Alps). This fact, as well as the circum- 
 stance, that they arc almost all cryptogenous or stratified crystal- 
 line rocks, which occur, on the one hand, as undoubted primitive, 
 and on the other as newer products, make it advisable to class 
 
 I 
 
bo'htogolbe,. under ,l,econ,m ^^ 
 
 »'■-; o- also of .,„ .:sn ,r ;:'• *.^ -^ptog»o. ^o™. 
 
 appearances. ■U'he.-eujwJl, i'" "T""^' "'"' <=°™p.«l. » Wo 
 
 -^ "I'ered sodi,„o„,a„, .,.,-ata ?■ ft ^ ".'" <""-^ '» ^e regarded 
 
 „ I' >» very evident fr„,„ n„ . ""^' '- ''■ ''«■" 
 
 ""= opinion tl,at „„ .. ^^^^ /"''''go'ng, tl,at .Vannuann lean, to 
 
 p'-oo. of »iidifleatii„ :/x";r'','' ""' ■■-"" °f '^ & 
 
 .;efa,n. from declaring hi„, / „" ° """ S'"'''' ""dcrwent. Ue 
 fe grounds n.ontion^t in ^Z^7' f ""^ '■''^»' P'^-PaHy o 
 '-nslafon of „ti„u ,,, »' j '■'!"- of I.is ..Lei.biel.j. , 
 
 Tio-gr„undsarotl,efoliatef, :?'"'■ ''" ""'^ J-™al.* 
 
 o( these phenomena f have .,lr„ , """'' "™ta- The first 
 
 ;'«". i» .l.e course of , f, f »«»•»'«' '» account for We 
 
 <™ whether the almost vo " l'^':™"" '"' »"J«"vo„r to a.c„ 
 ai» capahlo of being .,;Z:l ""'""" "' ""^ P"™itive strati L 
 
 -vpiained awa,, as i„ Ih, case of "r "•;"?"' ""'""°''''°"- »te 
 postpone .considering, „„, t ^ " "' 'r "-^'^^ »« '"'-'J '» 
 the latter rock. The .,«.„« 1 1! V T* "' ""* P'»"-"^io„ of 
 eaae of gneiss, „.ould of „„, ,," ! ""^ «P''™"«on adopted i„ the 
 oaso of the schistose roetr „ k'T 'r, '" '■"<'"''" ^ ■" the 
 ™;ca-schist and hornblende slaw "'"',"' "'''""">• ^-'' a. 
 atter rock was for-ned fro™ -ho , an It "'r""' "'«'"- "'»' «>« 
 .^^ f-«. l.at on the contrarv , j I °"h *'""" ""*"»' '^ 
 the lower ^one,, brought u,, to'le 1 n , '"■'"'""' "'■ ^°"« "f 
 .■-"'.encos, and consolidated ot J „e ""' "™"'J- ™-""aI 
 .1-'. of course, to the santc in „' e '^"' "^ """'• "'^■ 
 
 - have supposed in the cas,;,;:'"''?! ■';,-"'''''-'-■ » 
 
 * Vol. vi., p. 254. 
 
68 
 
 ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 formation of a thin crust of stratified rocks ; thosu rocks being 
 now to be found constituting the so-called primitive gneiss for- 
 mation. 
 
 In accordance with the views given in the second part of this 
 paper, of the nature of the process of soliditication at present pro- 
 gressing beneath the earth's crust, we must suppose that during 
 the solidification of the first crust, a contraotion of the volume of 
 the originally fluid material took place. This view must be 
 adopted on ex[>erimental grounds also. Bisohof found, in casting 
 a globe of basalt, twenty-seven inches in diameter, that in the 
 centre of the mass, on cooling, a cavity had formed capable 
 of containing half a pint of water. Further, at ihe Muld- 
 ner smelting works, near Freiberg, stones are cast of the slag run 
 out of the reverberatory furnaces. They are two feet long, one 
 foot deep and one broad, aiul when broken after cooling, they are 
 found to contain in iho middle irregularly shap^'d cavities from 
 three to five inches wide, the sides of wliich are covered with bril- 
 liant microscopic crystals.* From these instances it might be ex- 
 pected, tliat during the first solidification, a vacuum might, to some 
 extent, have been formed beneath the crust of the earth. With 
 the progress of th'-' consolidation tiie dimensions of the vacuum must 
 have increased, and the power of the crust to support the enor- 
 mous pressure of the tlien existing atmosphere must have decreased. 
 We may suppose that uUiniately a point whs reached, when the 
 crnst was unable longer to support the enormous load, and that it 
 then gave way in various phvces, its fragments sinking down to 
 the fluid interior and floating upon its surface. In this way the 
 first great subsidence of tlie earth's crust may be reasonably sup- 
 posed to have taken phice. The area of the original globe 
 having however decreased during the solidification, it would 
 be impossible for the fragments of the crust to maintain their 
 original horizontal position. Very likely also the still fluid 
 material beneath the crust Aould protrude itself through be- 
 tween the fragments, thrusting them aside, and limiling still fur- 
 ther the space occupied by the latter. Tiic consequence of this 
 would be, that the fragments would arrange themselves in posi- 
 tions more or less vertical, an 1, althoncrh some of them might still 
 remain horizontal, still highly inclined positions would be the rule. 
 We can even imagine how corrugations of the strata, such as 
 described by Sir William Logan in Canada, and by McCuUoch in 
 
 • Leonbard, Hiitlenerzeugnisse, p, 186. 
 
 
"WOW OF sm^ ,„„ 
 
 "VE AND PRnHASv Rooir. 
 
 69 
 
 8«'""'d, co„..l w ™""'*«^ WOKS. «o 
 
 I"™ "locate., ,•„ ,tt '^'"" "'^»» »f 'he alt ""'""^ *■-«= 
 
 ^'on'. their or,Vi„,X ,■'''.''•■ ''"•"«'■"'. "roa^ho,' ^k"""" ?'•«« 
 
 of the mnue of il „ ■ "='"" <» have sol.V) « 7 f™eti>red 
 
 "^T" "■« V It:"' '-- ?«-«:; C'f;"J''«- that 
 "'« ■■«'ati„;,,, „,■ „ ' "' "' «aotly ,!,„ ,„, ''"fJ part „f tj^ 
 
 h°".W»,w;.,cl,^,' „ ,7^V«,e.,tr,,a„f;t° °°''™<'<'»atthe 
 primitive m..K ,■ "'""'"'"•■m-.Mv .n. "* '''"'" »^i.W „vor. 
 
 •«- ».h„it ; ;:^''"-';>-t,-„ of „,:;, , /.r r '■""■' "^ ' « 
 
 ■■"•"•'»' overlai,, fcl ' " ^"«"'l-f.S,.„| f^' ""*ce. T;,„,, 
 
 f'-"" of the uL:,:? ""'" '"-'^•^ and r IT't'^ '"'"^ 
 •■"^on,,, ,,«,, „;';';«'■« are i„ ,,, " ^-"-'a the ve„,„al 
 
 O'OPS of the ,„V,,Lf;. r ""■ ■"""'^'•••■« V """■'■"' '"' 'he 
 
 °'«-'ai h«n.:e/j;,: ::.;"'-,., ,t,,, '■- e!:7 "" °»'- 
 
 'hey are overlaKl hv f t ," ''^'' ""^'- »« ""» "» -I i "o™"'''' ''^'^ 
 Fmmive roek,, „f ,.,,'"'""' ""•ata of t|,„ sil„" "'"»« areas 
 granite, ,,.„„:,,. ''™''. ™,„i„i„„ ," *"'"'-'ai> «, .,(„„,, j,, 
 
 •»^ -'h^zrrc'-^\->' '■»™M:i.fr.>'''^'-»-"''« 
 
 Of230^„„,,„,»' "" '"""leffree,,„f|„tn„, ""^';««e„d ""* 
 '•'<"» ^^to'ro ':'"■"-. ••» whiC, e„, ™: •:;'^ ^^veatread.^ 
 ««' «he,e r„ a- f:r '" -^'""^ '"-^rvaH r^' ""'■"•^ '"alined 
 -« '^'.-onahlv ;":7,r'''"'"j- «'™>e.l i tti,^!'"""'" ™PI'o« 
 
 Pifcal milee -^ "^ '"""• " "'W^e-'. of „„ ' "l '""'".?' '" 'heir 
 
 ««»«« p-«iti:r„'i r,:":r ""* ^^'a : i:"™ ^^ -"K 
 
 1«««»<»1 by the „r ,1* " ""'"""'• I'arlly hr ,),. ""•" "<« 
 ^ ffbbe ,n eoolioa "d partCL Ir"-^"""- «. 
 
 y "y 'he pratnsioo of 
 
70 
 
 ORiaiN OP ERUPTIVE AND PRIMARY ROCKS. 
 
 igneous matter from beneath tlie broken crust. An analogous 
 phenomenon may every winter be observed on the St. Lawrence, 
 When the ice shoves, pressure being exerted upon ic from higher 
 up the stream, the floes of ice are raised upon their ends, and a 
 confused aggregate of inclined beds is the rosult ; and it is worthy 
 of remark that each of these beds is in itself distinctly stratified, 
 just as are the individual layers of tlie primary rocks, the cause of 
 this stratification being in each case not entirely dissimilar. 
 
 "We have thus endeavoured to lomove Nauraann's principal ob- 
 jections to the igneous origin of tie primary stratified rocks. Wo 
 have next to refer to the objection founded on the mineraloglcal 
 composition of gneiss, which is the same as in the case of granite. 
 This objection is the presence in it of quartz, which occurs in such 
 a manner, as to indicate that it must have been the mineral which 
 soliditied last of all, although it is the most infusible of the constit- 
 uents of granite. Perfectly well formed crystals of it often, it is 
 alleged, leave their impn^ssion on the adjoining feldspar and mica. 
 We have already seen that this is denied by SarLorius von Wal- 
 tershausen, who also insists that the quartz formed subsequently to 
 the consolidation of the granite, by the action of water, must not 
 be confouuded with the original granular quartz, which is never 
 or seldom found crystiliizod. In spite, however, of this denial, 
 many supporters of the igneous origin of granite consider it ne- 
 cessary to attempt to account for the occurrence of quartz in the 
 manner above stated. The following are the remarks of Nauraann 
 on the subject : "Gaudin's experiments have shown that melted 
 silica becomes viscid before it solidifies, and while in this state it 
 may be drawn out into threads like scding wax. This proves that 
 the temperature, at which it solidifies, lies very far below the tem- 
 perature, at which it fuses, wherefore this phenomenon has been 
 used by Fournet in support of his theory of the surfusion of silica, 
 the fundamental idea of which theory has also been strongly sup- 
 ported by Petzholdt (Fournet, Compte Rendu, tome xviii. 1844., p. 
 1050 ; and Petzholdt, Geologic, p. 313). Moreover Durocher has 
 pointed out that the fusing temperature of silica (perhaps amount- 
 ing to 2800 degrees C.) is not necessiry in order to explain the 
 crystallization of granite, because the silica of the quartz formed, 
 combined with the elements of the feldspar and the mica, a com- 
 pletely horaogenous,igneous magma, in order to the fusion of which 
 atemperature approaching the fusing point of orthoclase may have 
 been suflScient. While the feldspar and mica crystallized from 
 
 
 i£- 
 
ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 
 
 71 
 
 this magma, the excess of silica was merely separated as quartz. * 
 These two explanations must not bo oonfounded with each other. 
 The surfusion of Fournet differs essentially from the viscosity of 
 Durocher. "En vortu du premier," says the latter philosopher, 
 " une substance peut conscrver sa parfaite liquidit<5, ii une tem- 
 perature infdriouie a son point de fusion. En vcrtu du second 
 des substances diverses, chauffeos jusqu'a liquefaction, puis abannou- 
 ndes au refroidissement spoiitannd, dana les m6mos circonstances, 
 mettent des temps fort indgaux a se solidifior, celles qui tendent a 
 crystalliser, deviennent solides les premieres ; celles qui constitu- 
 ent des masses araorphes restent longtcmps dans nn dtat plastique 
 analogue k celui de lapoix et intermdJiaire entre I'dtat liquideet 
 I'dtat 8olide."f When we take into consideration the common 
 blowpipe reaction, in which silica is often separated from a fused 
 bead as a gelatinous skeleton, it would appear to lend consider- 
 able support to Durocher's theory. 
 
 I here conclude the explanation which I have attempted of 
 the origin of the Primitive formation. I conceive that only one 
 series of rocks is entitled to this appellation. The term primary 
 has often been applied to quartzites and slates of later age ; which 
 rocks have been classified by German geologists under the name 
 of the Primitive Slate formation. It is very evident, however, that 
 there can have been but one primitive formation, and since the 
 slates and quartzites above referred to bear evidence of their having 
 been derived frem pre-existing rocks, it would appear incorrect to 
 entitle them primary or primitive. Were it not that geological no- 
 menclature is already sufficiently confused, it would appear much 
 more reasonable to apply the old term of Transition Formation to 
 these rocks; since it is highly probable that during the period in 
 which they were formed, the temperature of the first crust gradu- 
 ally decreased to a temperature at which it was possible for water 
 to exist in large quantity on the earth's surface. We have seen 
 that during the first granitic eruptions, water did not exist on the 
 surface, otherwise rocks of a more or less tufaceous character would 
 have been produced. This conclusion would also seem to be cor- 
 roborated by the ideas which we must entertain of the high tem- 
 perature of the newly solidified crust. When the temperature of 
 the latter so far decreased as to admit of the condensation of the 
 water existing in the atmosphere, the rain, which fell upon it, must 
 
 r 
 
 • Naumann, Lehrbuch, i., p. 740. 
 
 t Bui. de la Soc. Qeol. 1849-50, p. 276. 
 
f 
 
 72 
 
 ORIGIN or ERUPTIVE AND PRIMARY ROCKS. 
 
 ■■% 
 
 have been instantaneously evaporat; <l. This rapid condensation 
 and evaporation ran?! have continued through long ages before 
 any considerable accumulation of vfater could have taken place. 
 Even then such accumulations must have possessed for a long 
 time a boiling mperaj're, and long ages must again have been 
 necessary before it cooled downto )Uch an extent as to enable ani- 
 mated creatures to exist within it. If to these considerations wo 
 add thcfollowing,naraely thi.v the wnter condensing upon theheabid 
 rocks must have been charged with muriatic and carbt»nic ncids) 
 (the latter at a later s aore than the former), h is very j^'nin thr;'. 
 the pr'xluots of the action of thextmotjdieric iMiiu nces tlieii.must 
 have bfcon of a character widely ditl'oreiit from tliose produced by 
 the sar.ifl agencies at tho present day. The action of nch .vjd 
 ulat.e'^ water aidid 1)V heat must have l>een much more, energetic 
 then than now. I'liis lias b<;eii already fully rer'ogni?;od by Dr. 
 Hunt. "ThesoliiJ orus;." lio rcra-.rks, " would afterwards be at- 
 tacked by the acid-i, ^ vocipiint^'d, with water, under the pressure 
 o;' a high ;<tm<>.-,j)hj;iic •■ lumri, and at an elevated temperature ; 
 frori; which n'oyld iiisult tlie scparalion of a great amount cif silica, 
 and tlie formation of an ocean, whose waters would contain in the 
 state of chlorides and sulphaLes not only alkalies, but alf-> large 
 portions of lime an 1 magnesia. At a later period, the decompo- 
 sition of exposi-'l portions under the influence of water and carbon- 
 ic aeid v/ould give rise, on the one hand to clays, and on the o1 her 
 t ■' carbonate of soda. This latter reaction upon the calcareous 
 saiiAof the seawater must produce chloride of sodium and carbon- 
 ate oi lime. We have here a theory of the source of the quartz, 
 the carbonate of lime and the argillaceous matters of the earth's 
 crust exj)laining at the same time, the origin of the chloride of 
 sodium of thr' sea, and the fixation of the carbonic acid of the at- 
 mosphere ill the form of carbonate of lime."* I may be permit- 
 ted to remark, that no theory accounts more completely and satis- 
 factorily for the origin of the so-called Primitive Slate formation, 
 than does this. It is surely not too much to assume, that the 
 crystalline character of its rocks has been caused by the nature of 
 the agents then at work, and the influence of the higher tempera- 
 ture and greater atmospheric pressure then prevailing. It is evi- 
 dent that the action uf the muriatic acid of the atmosphere 
 must have long preceded the action of carbonic acid, since we 
 are almost unable to conceive that the latter gas could exist in 
 
 ^Canadian Naturalist, vol. vii., p. 202. 
 
 mic^ 
 
 becj 
 
 holid 
 
 hor'n 
 
 abov 
 
 hH 
 
 this 
 
 musj 
 
 gneii 
 
 werel 
 
U'" 
 
 On/fllN OF ERTTPlnvi!: AND PRTMART ROOKS. 73 
 
 water of higher than ordinary temperature. The quartz, the carboh- 
 ale of lime, and the argillaceous matter above mentioned are pecrt- 
 larly at Lome in the Primitive Slate formation, and are compara- 
 tively rare in the fundamental gneiss or primitive formation- 
 proper. We have only to refer to the highly qaartzose rocks of 
 the Huronian formation, of the Thelemarken quartz formation 
 and of the so-called primary sandstones of the western islands of 
 Scotland, to show that the separation of quartz on an extraordina- 
 ry scale must have been one of the first products of the condep, na- 
 tion of aqueous vapour on the earth's surface. Moreover, although 
 primary limestones are not of unfrequent occurrence in gneiss 
 they are of trifling extent compared with the limestones of the so 
 called Primitive Slates. At first of less frequent occurrence, of light 
 grey colour, and crystalline character, and evidently more the re- 
 sult of a chemical precipitation than loado np of animal organisms 
 they pass through various gradations of color, becoming more 
 frequent and of darker color (more charged with carbon) as they 
 grow younger. In the micaceous and the clay slates, which ex- 
 ceed in extent of developement both quartzitcs and limestones we 
 find a similar gradual change in their colours and lithological 
 characters ; the younger they become the more they are charged 
 with carbon, and the more they resemble slates of more modern 
 formations. The source of this carbon was undoubtedly the at- 
 mosphere, where it probably existed free, or was derived from the 
 decomposition of its compounds with otb^iir elements. Duringthe 
 period, when the primitive slate nx^ks wero formed, the metj^Uie 
 chlorides were also most prr»bably rv^movod from the atm<\»|\Wre* 
 This may have given rise to the extensive wetallkj d^>sit8 exist- 
 ing among these crystalline slat«es. 
 
 After the abrasion of tW x^i.-it^*-*^*! fK>m which the quartzose^ 
 micaceous and argillaceov.s sK%!^ iv^ulted, wo must suppose that it 
 became deposited in lifee hoJtow!^ ot" the then existing oriKst, which 
 hollows were most probaMy oov^pied by ]>rimitivo s*t,v%ta lying 
 horizontal or nearly so, Tho^^ parts of the first cr*»st, which rose 
 above this primitive ocean, are most likely to havo been the high 
 ly inclined primitive "^tTfatsi or eruptive masses of granite. Iy 
 this view be corr^t the»< the rocks of our Transition formation 
 must generally have bw>\ deposited conformably upon horizontal 
 gneiss, or ro<. ks allied to it. 
 
 Whilo the atmospheric agencies, and more especially water, 
 were thus at work upon the surface ot tlie. original crnst of the 
 
 P 
 
 mil. 
 
74 
 
 ORIGIN or ERVPTin AKD miMART ROOKS. 
 
 earth, the same process of solidification which we formerly re- 
 ferred to, must have been progressing beneath it. The interior 
 of the globe must have experienced a further contraction ; and 
 after having resisted for some time, the earth's crust must have 
 subsided, and become fractured and folded in the same manner 
 as the primitive gneiss, though perhaps to a less violent degree. 
 This idea of a gradual contraction of the globe, and the consequent 
 folding of the strata composing the crust, has especially been ad- 
 vocated by French geologists such as Rividre and Constant-Pro- 
 vost. The latter geologist has the following remarks upon it : 
 " Aprds des dissidences plus apparentes que rSelles, presqne tous 
 les gOologues tendsnt k admettre aujourd'hui, quo I'envtiloppe 
 consolidOe de la terre a OprouvO, et Oprouve encore, un mouve- 
 ment centripdte oontenu, dd k la diminution de chaleur et de 
 volume de la masse intOrieure du globe. De ce mouvenient il 
 r^sulte n^cessairement, dans I'enveloppe solide, et apr^s une r4- 
 sisteiice plus ou moins iongue, des ondulations, des plissemenls, 
 des r«dressemei)ts et des ruptures, dont les unes sont produites 
 diMK les «wrtiet> enfoTKi^es, >}t les autres dans les parties rclevdes 
 <ies plis^ C««c p*r ces pwitos que sont sorties les raati6res en- 
 ©pre m>*/9es «souj-jacente>-, elle« ont traverse les issues qui leur 
 ftaient aiomes, mais hIhb n'oni p(tb bris^ les barridres qui les re- 
 Sans doute qu'avec ces raouveraents g^n6raux des ap- 
 du sol ««rs le centre de la plauete, le refroidisse- 
 des ?etriuts loe»ux partiels dans les matidres re- 
 qiw la iiTminutien in^gale des matii^res de nature di« 
 ■ a Ogaiemeiit. donne IWu a des cbangcments relatifs de r.i- 
 i<flit; 4 ii«& rupcares qt3el<qutifois tr^s-importantes ; que souvent 
 le fimtfemtamt de tables horizontales a pu occasionnor dee 
 pr«wiion& iatenues qui ont pouss^, de dedans ou en dehors, des 
 VMtidres mail^tebles e^ sons inverse de celui determine par la 
 grande CAmti preasn^ du mouvement, lesquelles matidres 
 ont pu Tedr^iBser, WMiwrser. soulever les lambeaux des strates 
 brisks. MtRs oe wsft la aes faits de detail, des exceptions qui, 
 loin dMnfirmer la ^i g^i^rale, viennent la confirmer, lorsqu'ils 
 sont analyses avec aifjt^eution et reduits k leur juste valeur.''* In 
 describing and accounting for the architecture of the " Terrain 
 gn6i8sique de la Vend6e" Ri/iAre adopts the same theory .f 
 
 * Oon3tant«Pr^rost, sur le mode de formatioa dea chatnes de monta- 
 f nes. Bui. de la Soc. (3^ol. de Franc*, 1849-60, tome vii, p. 53. 
 t Bui de la Soc. Geol., 2 >eri««; lome vii , p. 927. 
 
 I 
 
ORIGIN OF BRUPTIVB AND PRIMARY ROOKS. 
 
 76 
 
 •'ils 
 
 We may now proceed to consider what effocta, according to 
 this Iheory, would be produced on the oarth'a crust as the same 
 was constituted after the slate rocks above mentioned, and even 
 the ao-i-alled groywacke series had been deposited. The slates 
 and sandstones of the latter formation are tlie oldest rocks whioh 
 thoroughly resemble, in their lithological characttirs, the sedimen- 
 tary deposits of later periods ; wherefore wo may suppose that at 
 the same time they wore formed, the temperature of the earth's 
 surface and the agencies at work upon it somewhat iipproxi- 
 mated to those of the prasont day. The portion of the earth's crust 
 least likely to be aflfected by the subsidences consequent upon the 
 contraction of the globe, may reasonably be supposed to have 
 been the thickest part, that part where vortical strata of gneiss and 
 rocks allied to it, extended deep down into the earth's crust. The 
 part most liable to be fractured and raised into folds, would moat 
 probably be the thinnest, or that part where horizontal or but 
 slightly inclined gneiss strata, had been conformably overlaid by 
 micaceous, argillaceous, chloritic and quartzose slates. If we at- 
 tempt to speculate as to what might be the first consequences of 
 the contraction upon these latter rooks, we would naturally sup- 
 pose that after a fissura had once been formed, the strata border- 
 ing on it would rise in a manner s)cetched in the subjoined figura. 
 
 b a b 
 
 a. gneiss, b. mica schist, c. clay alate. 
 And in reality not a few of the so*called Primitive Slate districts 
 possess an architecture closely analogous to the above ideal sec- 
 tion. This is especially the case in the Alps of Salzburg and 
 Upper Carinthia. In this part of the central Alps, according to 
 Credner, a mass of granitic gneiss, drawn out from east to west, 
 forms the centre. On the north as well as on the south side of 
 this mass crystalline slates overlie it. On the north side the dip 
 is at a high angle to the north, and on the south side the highly 
 inclined strata dip to the south. These crystalline slates arc 
 divisible into three groups, the lowest consisting of common and 
 calcareous mica-slate, the middle group of chlorite and talc slates, 
 and the upper group of common and calcareous clay-slate. More- 
 over the structure of the metamorphic rocks of eastern North 
 America, and also of the slato diatricta north of the Mjo'ien in 
 
t 
 
 ,76 
 
 OBIOIN OF ERUPTIVE AND PRia^ARY ROOKS, 
 
 Norway, would ueeui greatly to rcsombiti the above idtju' iiootioii, 
 if wo suppose otiu litilf of the same to be oblituruted. The follow 
 .iog is a section of the Alle<;^hatiy chain nccordiug to Kogum:* 
 
 i 
 
 1. Gneisa, mica slate, &c. 
 
 2. Silurian sjatom (so-called motamorpiilc strata). 
 
 3. Devonian " 
 
 4. Oarboniferoud " 
 
 The above delineated structure of the slate rocks would have 
 experienced a modification, in the event of igneous rocks having 
 been protruded through the fissures formed by these movements 
 of the earth's crust. These igneous rocks would most easily be 
 protruded at the point marked A in the sketch first above given. 
 If we imagine a granitic mass to be erupted at the point so mark- 
 ed, we have then a section resembling in its general features the 
 build of the so called primitive rocks in many parts of the Alps 
 of Switzerland, in the Saxon Erzgebirge, in Hungary, and in the 
 gneissoid region of La Vendee, above mentioned. The following 
 is a section given by Beudant, of the structure of the schlsLose 
 rocks in the county of Giimor in Hungary .f 
 
 123436863636 7 6 8 8 8 
 
 1. Granite. 
 
 2. Gneiss. 
 
 3. Mica-schist. 
 
 4. Greenstone. 
 
 5. Limestone. 
 
 6. Clay-slaie. 
 
 7. Iron ore. 
 
 8. Schistose greywacke and limestone. 
 
 Here the primitive and slate strata rest upon the granite in the 
 following order : 1st gneiss, 2d mica-schist, 3d clay -slate. The 
 
 • Naumann, Lehrbuch, i, 994. 
 
 t Voyage en Hongrie, Atlas, Fig. 5. 
 
 I 
 
OSK^IN OD .ERUPTIVE AND PRIMARY ROCKd. 
 
 ,17 
 
 n, 
 w 
 
 5Z^ 
 
 iiavo 
 
 vini; 
 
 iienla 
 
 ly bo 
 
 ^iven. 
 
 oaark- 
 
 39 the 
 
 3 Alps 
 
 in the 
 
 lowing 
 
 hiatosa 
 
 aite in tbe 
 ate. The 
 
 inioa-sobiHth uud clay-ilutusiit the disu. i'^ ^bovti uiuntionod niivur 
 occur oveilylug the gneiss dtrata uncoiit'ormably. On the contrary, 
 tliey are so intiriifitely connected that a gradual transition ia <r«ner- 
 ally observed to take place between them ; the gneiss gradually 
 changes into mica-ichist, the latter gradually becomes less crys- 
 talline, and finally ■irgilJuoeous and obloritiu rocks result. 
 
 A further modification of the above type of the structur« of 
 the slate rocks occurs when the granite is so extensively protruded 
 as to overlie the gneiss strata, or when the latter have not been 
 forced up to the surface. In this case the micaceous or argilla- 
 ceous slate is found immediately reposing upon or at least in con- 
 tact with the granite. In this manner the mica-schist with inter- 
 stratified limestones, north of Drontheim in Norway, overlie the 
 granite of Vestfjord, and in this way also the kilias or clay-slates 
 of Cornwall lean upon the granite of Dartmoor. In the latter 
 cases no lithologioal transitions are observable between the 
 slates and the granite, while in former cases, where gneiss is in- 
 terposed between them, the transition from the latter rock to 
 granite is distinctly observable. This phenomenon, it will be 
 observed, however, is not inconsistent with the explanation here 
 given of the origin of these rocks, 
 
 I have thus attempted to explain some of the most remarkable 
 phenomena connected with the primary rocks. It will be obser- 
 ved that in so doing, I have tried to elaborate and combine toge- 
 ther many of the id^is expressed by difterent geological authori- 
 ties. I am far however from maintaining that the theory here 
 given is adequate to account for all the facts observable in connec- 
 tion with these rocks. Nor is it at present necessary that this 
 explanation should be perfect. There must be in geology as in 
 other sciences, obscure problems always awaiting solution. The 
 best apology which I can offer for presuming to atterapi mn 
 explanation of the enigmatical phenomena connected with iha 
 primary rocks, is in the following words of McCulIoch :* •' The 
 human mind is so constituted that it cannot rest content" with 
 facts. If it posesscs innate propensities, the investigation 
 of causes is assuredly one of them. The very geologist who 
 disclaims all theory has his own ; the lowest of the vulgar 
 desire reasons. The laws which govern the phenomena of na- 
 ture force themselves irresistibly on our attention. They are 
 ■trictly involved with the analogies which regulate all our reason- 
 
 * Sjatem of Geology, vol. i, p. 485, 
 
I 
 
 u 
 
 ORiaiN OF IRUPTIVE AND PRIMARY ROOKd. 
 
 ingR and direct our dbsorrations ; and without them we cannot 
 proceed a stnp on firm ground. They distinguitth the pbilotto- 
 pber from the empiric, and combine scattered observations into 
 a body of useful and rational science. Even in the science of 
 nature, as in that of numbers, the assumption of imnginary or 
 erroneous lavr», leads to the discovery of the truth. The history 
 of astronomy is in itself a lesson to those who ignorantly uo* 
 dorvalue the pursuit of general lawH. Bewildered in spheres and 
 vortices, it arose, as in a moment, complete, from the theory of 
 gravitation. 
 
 " Hence the consideration of secondary causes, forms, not only 
 « legitimate, but an essential part of geological science. That 
 science, like all others, comprises the history of all the facts which 
 it involves ; and from these, it establishes certain general analo- 
 gies. Ascending a step higher it declares the laws which have 
 regulated, and will continue to regulate, all the phenomena of the 
 globe; and thus finally establishes a legitimate theory of the 
 earth." 
 
 No trace of organic remains has been discovered in these mica* 
 oeous, chloritic or argillaceous slates, nor even in the limestones 
 associated with tham. The adherents of the metamorphio 
 hypothesis attempt to account for thi:) by supposing that the fos- 
 sils have been obliterated by the agencies whioh have effected the 
 alteration. But even in the greywackc slates and sandstones, 
 traces of life are rare; and it is only in the very newest strata of 
 that series, that they become at all frequent, and then they 
 belong to the inferior grades of animal organisms. That the air- 
 breathers, recently described by Dr. Dawson, first make their 
 appearance in the coal-measures, may bo regarded as a proof of 
 the absence of free oxygen from the atmosphere which existed 
 daring the deposition of the Lower Silurian rocks. Not until the 
 carbonic acid was to a great extent removed from the atmosphere 
 by the luxuriant vegetation of the coal period, and its place taken 
 up by oxygen, was it possible for air-breathers to exist. The 
 extraordinarily rich vegetation of that epoch was no doubt stimula. 
 ted by the immense quantities of carbonic acid in the atmosphere, 
 and the exceedingly warm climate which then prevailed over the 
 whole surface of the earth. This warm climate, we are justified 
 in supposing, was caused more by the radiation of heat from tha 
 interior of the earth, than by solar influence. So that it is possi- 
 ble to trace a coBoectioa between the phenomena of internal heat 
 
oRifliH Of nmrrvt and pmmaiit rocks. 
 
 79 
 
 .0 
 
 of 
 or 
 
 ry 
 
 in- 
 
 of 
 
 mly 
 
 'hat 
 
 lich 
 
 lalo- 
 
 have 
 
 ■ the 
 
 f the 
 
 mica- 
 stones 
 prphio 
 le fos- 
 ed the 
 ones, 
 rata of 
 they 
 le air- 
 their 
 roof of 
 existed 
 ntU the 
 ospliere 
 taken 
 i. The 
 stiroula. 
 losphere, 
 over the 
 justified 
 from th« 
 is posai- 
 trnal heat 
 
 'A 
 
 and the charaoteristio fttrata of the carbon iforouH (tystem, and 
 between that serins of rockH and the constitution of the primitive 
 HtmoHphere, In this, as in much of what has been Hinted in this 
 paper we recognise how intimately linked together all natural 
 phenomena and all departinents of science are. The various natu. 
 ral sciences are like the crystalline rocks; they graduate into each 
 other, forming, when properly interpreted, a compact, well ordered 
 and harmonious whole. 
 
 And while we study and recognise all thi«, surely it behoves us to 
 acknowledge reverently the great Author of all. The mere exter* 
 oal features of primitive di-^triots inspire us with feelings of 
 wonder and awe. Standing on the summit of Gaustaf jcld, we nan 
 look northward over humlreds of square miles of primitive rocks, 
 forming there the broad, barren plateau of Ilardangerfjold. As 
 far as the eye can roach there is spread out a desert of rocks 
 broken only by the lakes, which form the sources of the turbulent 
 streams that leap down into the fiords of the west and south, or 
 by valleys with precipitous sides, which seem as if hewn out of 
 the solid rock of the j lateau beneath the level of its general 
 surface. The scanty and stunted vegetation heightens the desola- 
 tion of the scene, but nevertheless its rugged grandeur causes the 
 observer to be deeply impressed with his own insignificance, and 
 with the awful power of the Originator of the universe. But 
 how greatly is this feeling deepened when the architecture of 
 these rocks and the mode of their formation is considered. Here 
 we feel oar utter littleness even more forcibly ; but we at the same 
 time gain some idea of that series of processes and revolutions by 
 which the earth was fitted for man. and of the power and wisdom 
 of the great Designer who caused our present beautiful earth to 
 emerge from the chaos of the primitive period. Wo also learn 
 enough to exclaim with the Psalmist, " Of old Last Thou laid the 
 foundations of the earth." 
 Acton Vale, C. E. 
 
 12th January, 1864.