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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 ® . 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 e 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) 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.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 innly 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 lyinf,. 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 Hrmacuti **■ 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 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 mhall 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 lluioured 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. Guinanis, 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 nminij 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*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, 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 het )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. 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\' 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 developc8oid 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 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 thtlf 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, liiove 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; 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 ;.-,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 */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- ieri««; 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