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Maps, plates charts, etc., may be filmed at different reduction ratios. Those too large to be entirely included in one exposure are filmed beginning in ths upper left hand corner, left to right and top to bottom, as many frames as required. The following diagrams illustrate the method: Les cartes, planches, tableaux, etc., peuvent 6tre film6s d des taux de reduction diffi§rents. Lorsque la document est trop grand pour dtre reproduit en un seul clich4, il est filmi i partir de Tangle sup^rieur gauche, de gauche d droite, et de haut en bas, en prunant le nombre d'l'^ages ndcessaire. Les diagrammes suivants illustrent la mdthcde. 1 2 3 1 2 3 4 5 6 w-vic.^'^ «-^«!p tt^tt-'d CONTRIBUTIONS TO LITHOLOGY. Z ^ ^^-iX^/ I. THEORETICAL NOTIONS. II. CLASSIFICATION AND NOJIENCLATURR. III. ON SOME ERUPTIVE ROOKS. IV. LOCAL METAMORPHISxM. BY T. STERRY HUNT, M.A., F.R.S., OF THE OEOLOaiCAL SUHVKV OF CAK^DA. llEt^nlNTED FRO:*{ SiI.LIMAn's JoURNAI. FOH MARdrt AND Jn.Y 1864' I MONTREAL 1864. I t ent rocks. I have thought it well to give at some length the remarkable results and conclusions by Mr. Sorby, because I conceive tbatthef have not as yet received the full degree of consideration to which they are entitled, and are perhaps little known to some of m-^ readers.* The tempera.are deduced by him from the examination of the crystals of hornblende and feldspar from Vesuvius is curiously supporte-l by the experit^ents of D:\ubr4e; who obtained crystallized pyroxene, feldspar, anc quartz, iu presence of alkaline solutions, at a temperature of V f redness; while De Senarmoiit trystallized quartz, fluor-spar, and sulphate of barytes in presence of water, at ieraperatures between 200" and 300" C. At thesame time the deposits from tho thermal waters at Plombieres show thst crystalline hydrous silicates, such asapophylliie, harmototiac, and chabazite, have formed at temperatures but little aoove 80° 0. Vie conceive that the deeply buried sedimentary btrata, under the combined action of heat and water, hav^ according to their composition, been rendered more or less plastic, and in many cases have lost to a greater or less degree the marks of their sedimeti- tary origin, although still retaining their original stratigraphical position. In other c ases they have been displaced, and by pres- sure forced among disrupted strata, thus assuming the form of eruptive rooks ; which, becoming consolidated under a suffideht pressure, retain the same mineral characters as in the parent beds. It is only those rocks which, like lavas, have solidified at or Hear the sur'ace of the earth, and consequently under feeble pressure which present mineralegical characters dissimilar to those of the undisturbed crystalline sediments. With this exception^ the only distinction which can be drawn between stratified and unstratified masces must in most cases be based upon their attitude, and' their relation to the adjacent rocKs. In view of these considerations I have, in previous papers, adopt- ed for geological purposes a division of crystalline rocks into '"See further the late observations of Zirkel confirming those of Sorb'/ Proc. Imp. Acad. Vienna, March 12, 1863 ; in abstract in Quar. Jour. Geol. Soc. vol. xix. 8 indigenous rocks, or sediments altered in situ, and exotic rocks, op sediments displaced and translated, forming eruptive and intrusive masses. T"^ ider the head of exotic rocks is however to be included another class of crystalline aggregates, which are for the most part distinguished by their structure from injected or intrusive masses. I refer to the accumulations which fill mineral v^ins, and which doubtless have been deposited from aqueous solutions. While their peculiar arrangement, with the predominance of quartz and non-silicated species, generally serves to distinguish the contents of these veins from those of injected plutonic rocks, there are not wanting oases in which the predominance of feld- spar and mica gives rise to aggregates which have a certain resemblance to dykes of intrusive granite. From these however* true veins are generally distinguished by the presence of miner- als containing boron, fluorine, phosphorus, coesiura, rubidium, lith- ium, glucinum, zirconium, tin, columbium, etc. ; elements which are rare, or found only in minute quantities in the great mass of sediments, but are here accumulated by deposition from waters, which have removed these elements from the sedimentary rocks, and deposited them subsequently in fissures. No one at the present day will probably be found to deny the plutonic origin of most non-stratified rocks, so that the once vexed questions of the neptunists and plutonists may be regarded as set- tleo. If however we go back but a few years in the history of geology, it will be found that an eruptive origin was theu claimed for many ocks which are now admitted to be indigenous. It is scarcely necessary to refer to the views of those who have main- tained the exotic character of many quartzites and crystalline limestones, when a, majority of writers, even to the present day, class serpentines, euphotides, and liyperites among eruptive rocks; although the experience of every field-geologist is accumulating, from year to year, a great mass of evidence in favor of the indige- nous nature of all these rocks. The sedimentary and indige- nous character of very many granites, syenites, and diorites will now no longer be questioned. Thus we find, for example, that the melapliyres of the Tyrol, which, in Von Buch's too-famous theory ot dolomitization, were supposed to have been erupted to- gether with magnesian vapors which effected the alteration of the adjacent limestones, hav'> been shown by Fournet to be sedi- ments of Carboniferous awo, metamorphosed in situ^ — indigenous ! 1 9 rocks, which were altered before the Jurassic dolomites were de^ posited (Bui. Soc. Geol. France [2], vi, 506-516). In Ike manner we find Scipion Gras concluding from his researches on the anthractic rocks of the Alps, that the serpentines, euphotides, por- phyries, and spiiites, which are there found associated with crys- talline schists, are all of sedimentary origin, but have been so pro. foundly r,ltered in situ as to have lost nearly all traces of sedimen- tary ong,n. (Ann. des Mines [5], v, 475.) We might add that tlie tendency of recent investigations has been to show that the protogines, or granites of the summit of the Alps, are Tertiary strata altered m place ; thus confirming the bold assertion made by Kef- erstein m 1834, that these granites are altered strata of fysch. (Tm Journal [2], xxix, 123, 124.) Lesley's recent investigations of the granites of the White Mountains of New Hampshire, show them to be clearly stratified sedimentary deposits in nearly hori- zontal layers. (American Mining Journal, I861,page 99; Silliman's Journal [2], xxxi, 403.) The ophites (amphibolites) of th« Pyre- nees, which by Dufrenoy and other French geologist^* have been regarded as eruptive, and were by the fo.mer imagined to be in some mysterious manner related to the rock-salt and gvpsum of the region which he supposed to be, like the ophites, of posterior origin to the enclosing strata (Expiic. de la Carte Geol. de France, ',96) are according to a recent note by Virlet, not eruptive, but altered indigenous rocks ; belonging, together with (ho associated gypsum and saliferous strata, to the Triassic series. (Comptes Kendus de I'Acad., Aug. 1863, p. 232). • It would be easy to multiply examples of this kind, which show that a careful study of very many oi the crystalline rocks hitherto regarded as eruptive, leads to the conclusion that they are really indigenous rocks. At the same time, many of these indigenous rocks appear to have been at one timo in a soft semi-fluid con- dition, which permitted movements obliterating the marks of sedimentary origin, and producing other results which show the passage into eruptive rocks. Thus the crvstalline limestones of the Laurenlian series in Canada are frequently interstratified with thm beds of gneiss and quartzite, both of which are often found broken, contorted, and even twisted spirally, in a manner which ndicates great flexibility of the silicious layers, as well as violent movements in the nalfflrAnnQ r«ni, ti,« i-f.__ .-_ _• » J. ' — ■■"" ~"^ 1 alter 13 III sum u cases found in the form of thin seams or considerable dykes among th«k 10 adjacent broken ailicious strata ; thus assuming for small distanced, tlie characters of an intrusive rock. For some figures and descrip- tions illustrating these broken and distorted strata, see Geology of Canada, pp. 21, 28. We may ako allude in this connection to the observations of Dr. Hitchcock among the altered strata of the Green Mountains, which seem to show that the pebbles of gneiss and of quartz in certain conglomerate beds have been so softened astohave been flattened, laminated, and bent around each other. (Silliman'a Journal [2], xxxi, 372.) Hence, while the tendency of the various observations above cited is in favor of the indigenous character of many rocks hitherto regarded as eruptive, we have at the same time evidence that these rocks are occasionally displaced. We should not therefore on a-priori grounds reject the assertion that any raetamorphic sediment may sometimes occur in an exotic or intrusive form. A given rock, like limestone or diorite, may occur both as an indigenous and exotic rock; and different por- tions of the same mass may be seen bydifferent observers under suet unlike conditions that one may regard it as indigenous, and the other, with equal reason, may set it down as intrusive. It is evu dent then that to the lithologist, who examines rocks without reference to their geological relations, the question of the exotic or indigenous character of a given reck is, in most cases, one alto- gether foreign ; and one which can frequently be decided only by the geologist in the field. Hence, although generally made a fun- damental distinction in classification, it will be disregarded in the following sketch of the nomenclature of crystalline rocks. I may here allude to a fact which I have already noticed, and tried to explain, (Silliman's Journal [2], xxxi, 414, and xxxvi, 220,7iofe,) th&t throughout the great raetamorphic belt which constitutes the Appalachian chain, exotic rocks are comparatively rare (at least in New England and Canada) ; but abound, on the contrary, among the unaltered strata on either side. Illustrations of this are seen in the valley of Lake Champlain, and in its northward continuar tion toward Montreal, in those of the Hudson and Connecticu*, »nd in the northeastward continuation of the latter valley by Lake Memphramagog to the Bay of Chaleufs, which is marked througlx- out by intrusive granites. In accordance with the reasons already assigned forihis distribution of exotic rocks, it is probable that a similar condition of things will be found to exist in other regions ; and that eruptive rocks will, as a general rule, be found among 11 i unaltered, rather than among metaraorphic strata. It is of course possible that a crystallization of the sediments may in some cases take place subspquent to the eruption of foreign rocks into their midst. The rarity of intrusive rocks among crystalline strata, not less than the unaltered condition of sediments which are tra- Tersed by abundant intrusive masses, is a strong proof of the fair lacy of the still generally received notion which connects meta- morphism with the contiguity of eruptive rocks. II. Classification and Nomenclature. It is proposed in this second part, to describe briefly the com- position, structure, and ncraenclature of the various crystalline silicated rocks, considered without reference to the distinction be- tween indigenous and intrusive masses. Comparatively few of these rocks are homogeneous, or consist of a single mineral species and the james which have been applied to varying mixtures of different species are of course arbitrary ; and as they have often been given without any previous mineralogical study, it some- times happens, that, as in the case of the rocks composed of anorthic feldspars and pyroxene, different names have been pro- posed for varieties very closely related, or differing from oae another only in texture or in structure. The minerals essential to the composition of the rocks under consideration are few in number, and are as follows : quartz, or- thoclase ; a triclinic feldspar which may be albite, oligorlasCf andesine, labradorite, or anorthite ; scapolite, leucite, nepheline sodalite ; natrollte, or some allied zeolite ; iolite, garnet, epidote, woll^stonite, hornblende, pyroxene, olivine, chloritoid, serpentine, diallage ; rauscovite, phlogopite, and some other micas ; chlarite, and talc. To these may be added as accidental ingredients, the car- bonates of lime magnesia, and protoxyd of iron, together with magnetite, ilmenifce, and sphenc. The silicates which, like tourma- line,, beryl, zircon, spodumene, and lepidolite, contain considerable portions of the rarer elements, and often otcur with quartz and feldspar in granitic veins, whose origin has already been alluded to, enter at most in very small quantity into great rock-massea. . .... T •■ • .._•*'* r--» » •! cvi it'/ift* I V Mi "- s Y "i-t*' i * s**j ■ ■> -» 'r*.?-* ••• ** w*-,w deserving of notice as they have led to a greait multiplication of names. We may note first the granitoid stricture, in which the mineral elements are distinctly crystalline, a. in sfranite. From I 12 this, there is a gradual passage through granular into compact tarielies of rock. Most of these are simply finely granular, and are rightly entitled to the distinction of crypto-crystalline ; but others, like the pitchstones, obsidians, and lavas, are apparently amorphous, and are natural glasses. In some cases the constituent minerals may be so arranged as to give a schistose or agneissoid form to a rock. This arrangement is generally to be looked upon as an evidence of stratification ; but something similar is occasionally •bserved in eruptive masses. In the latter case it generally seems to arise from the arrangement of crystals during the movement of the half liquid crystalline mass ; but it may in some instances arise from the subsequent formation of crystals arranged, m parallel planes. See on this point Naumann On the Probable Eruptive Origin of Several Kinds of Gneiss, etc. ; Leonhard and Bronn, Neues Jahr- buch for 1847, and Poulett Scrope, Geol. Journal, xii, 345. I consider however that their views are to be adopted with great re- serve, and admitted only in a very few cases. The ribbanded struc- ture of some porphyries and clinkstones, as noticed by S.rope, is undoubtedly the result of movements in the liquid mass, and the. same is true of some of the granitoid dolerites to be described in Ine third part of this paper; but the eruptive origin assumed by Darwin, Naumann, and some others for great areas of gneiss and gneissoid granite, seems to a student of the crystalline rocks of this- continent utterly untenable. As has been already remarked, the progress of each year's investigation restores to the category of indigenous rocks many of those previously regarded as eruptive, and will, I am convinced, cenfirm the principle which I have laid down of the comparative rarity of exotic rocks in crystalline and in rnetanorphic regions. Occasionally the crystallization of a rock takes places around cer- tarn centres, giving rise to rounded masses which have a radiated or a concentric structure, and constitute the so-called globular or orbi- cular roi.ks. Distinct crystals of some mineral, generally feld- spar, augite, or olivine, are often found imbedded in rocks having a compact base. To such rocks the name of porphyry is given, and by analogy a rock with agranular base enclosin/dislinct crystals isdesignated as porphyritic or porphyroid. Amorphous or vitreous reeks, fis pitchstones, are In like manner sometimes porphyritic. The name of porphyry, at first given to a peculiar type of fold- 13 spathic rocks, has now become so extended that it is to be regarded as only indicating an accident of structure.' The title of amyg- daloid is given to various rocks having rounded cavities which are wholly or partially filled with various crystalline minerals. The base of these rocks is generally granular or crypto-crystalline ; but is sometimes amorphous, resembling a scoria or vesicular lava, the cavities of which have been filled by infiltration. Such is doubtless the origin of some amygdaloids. In more cases how- ever these cavities have probably been formed like those often found in dolomites, and in some other rocks, by a contraction during solidification. Porphyroid rocks, in which quartz, orthoclase, and other raineials are arranged in orbicular masses, are also Fometimeg designated as amygdaloids, and may be confounded with the two previous classes in which the imbedded minerals are the result of subsequent infiltration. Allied in strucure and origin to the last are what are named variolites or variolitic rocks. (See Geology of Canada, pp. 606, 607.) The masses into which some aluminous minerals enter as a prominent element constitute by far the greater part of the rocki now under consideration. These are n-.turally divided into two classes, whose origin we have pointed rut in a recent paper already referred to. (Silliman's Journal [2], xx ;vi, 2 18.) The first of these is characterized by containing an excess . f silica, with a portion of alu- mina, much potash, and small portions only of lime, magnesia, and oxydof iron. The second class contains a smpller amount of silica and larger proportions of alumina, lime, magnesia, and oxyd of iron* with soda, and but little potash. These chemical differcuces are made apparent in the more coarsely crystalline rocks, by the nature of the constituent minerals ; and in the compact varieties, by differ- ences in color, specific gravity, and hardness. Thus in the rocks of the first class the predominant mineral is orthoclase, generallv asso- ciated with quartz, and the composite rocks of this class seldom have a density much above that of these species ; or from 2.6 to 2.1. In the second class, the characteristic mineral is atriclinic feldspar with pyroxene or hornblende, the feldspar sometimes predominant *; while in other cases the pyroxene or hornblende makes up the principal part of the rock. The presence of these latter minerals generally gives to the fine-grained rocks of this class a dark c^Ior, a hardness somewhat inferior to the more siHcioua class, and .• density which may vary from 2.1 to more than 9,0. It will 14 however be found that the line between the two classes cannot always be distinctly drawn: inasmuch as rocks containing, orthoclase and quartz often include triclinic feldspars such aa albite and^ oligoclase, and by an admixture of hornblende oflfer a transition to rocks of the second class. On the other hand, quart* is sometimes found with triclinic feldspars and hornblende in the rooks of the second class. Besides these two feldspathic clashes, there is a third small but interesting group, in which an aluminous silicate of high specific gravity, such as garnet, epidote, or zoisite replaces the feldspar wholly or in part. These minerals being basic silicates rich in alumina, the relations of this group are naturally with those of the second class, although yarieties of these species are found in rocks which belong to the first class. The silico aluminor.? crystalline rocks may thus be convenient- ly divided intotliree families. The first of these includes those rocks in which the aluminous mineral is orthoclase (orthose), from which ihey may be conveniently designated by the name of the orthosite family. The second includes those in which the altt- minous elemenr is an anoithic or tiiolinic feldspar, and may be designated as the a«orv,.>^t. t i ^s^^ -^ • 224: ; Geol. of Canada, 688.) In most cases howerer, titjse ffeld- B 18 spars are intermingled with some other mineral, commonly horn* blende or pyroxene. The name of diorite is by good authorities restiicted to rocka whose predominant elements are triclinic feldspars with hornblende; ■while the names of diabase and dolerite distinguish those rouka in •which pyroxene takes the place of hornblende. In some anortho- site rocks however, pyroxene and hornblende are intimately associated, so that a passage is established from diorite to dia- base. The feldspar of diorites varies in composition from albite to anorthite, and is occasionally accompanied by quartz. This, though most frequent with the more tilioious feldspars, is some- limes met with in diorites which contain feldspars approaching to anorthite in composition. Sometimes the two constituent minerals are distinct and well crystallized, constituting a granitoid rock : fine examples of this, hereafter to be described, occur in the intru- sive hills of Yamaska and Mount Johnson. At other times the diorite is finely granular or compact, when its color is generally of a green more or less dark from the disseminated hornblende, and it takes the name of greenstone. The greenstones of the Huronian series are in part at least diorites, and probably indige- nous; but a great number of the so-called greenstone-traps are pyroxenic, and belong to the class of diabase or dolerite. Diorite not unfreqnently contains a mica,which is generally brown or black in color. Chlorite, magnetite, ilmenite, and sphene often occur as disseminated minerals, as also carbonates of lime, magnesia, and oxyd of iron. The finer-grained diorites are frequently porphy- ritic from the presence of crystals of feldspar or of hornblende. Occasionally this rock is concretionary in its structure, as in the orbicular diorite or napoleonite of Corsica ; which contains a feldspar allied to anorthite, with hornblende, and some quartz. The norite from Sweden is a granular mixture of a similar kind, containing also mica ; and the ophite of some writers is a diorite in -which hornblende greatlv predominates. The rocks which are essentially composed of anorthic feldspar and pyroxene, present still greater diversifies than the diorites, and have received various names ba^ed upon differences in texture and in the form of the pyroxenic element. It is here proposed to re- strict the name of dolerite to such of these rocks as contain the blank auoritiu variety of nvroxene. and to inr.lndft the mixturea of triclinic feldspars with all the other varieties of this species uuder 19 the head of diabase. The finer-grained and impalpable varieties of diabase have received the name of aphanite ; which is often indis- tinguishable from the corresponding forms of diorite, and like these may become porphyritic, giving rise to the angite-porphyry of some authors. Diflferent varieties of this porphyry have received the name of labradophyre, oligophyre, and albitophyre, according to the composition of the imbedded feldspar crystals. These are sometimes accompanied by crystals of augite, or are altogether replaced by tliera. The came of hyperite or hypersthenite has been given to those varieties of diabase which contain hypersthenc or diallage. These rocks occur abundantly in the Labrador series, where the hypers- thene in them sometin ^s takes the form of a green diallage, or passes into a finely granular pyroxene, and is associated with red garnet, ilmenite, and a little brown mica ; in addition to which epidote is said to occur in the hyperites of the came series in New York, and olivine is mentioned as being found in the hyper- ites of Sweden, and of the Island of Skye. Hornblende is also in some localities associated with the hypersthene. The hyperites, although indigenous rocks in the Labrador series in Canada, are described as forming in other regions intrusive masses. Those varieties of diabase or hyperite which contain dialTage, have, by the Italian lithologists been called granitone, but by Rose and others have been described under the name of gabbro. This rock sometimes contains hornblende, mica, and an admixture of epidote. A compact white or greenish-white epidote, or zoisito, which has the hardness of quartz and a density of 3.3 to 3.4, is the mineral named saussurite. This with smaragdite, which is an emerald-green pyroxene, often minged with hornblende, and passing into diallage, forms the euphotide of Hauy. Com. pact varieties of labradorite and of other triclinic feldspars have by- most of the modern lithologists been confounded with saussurite and hence the name of euphotide is frequently given to the so- called granitone or gabbro, whish is only a diallagic variety of diabase. The true euphotide often contains a portion of talc, and sometimes encloses crystals of a triclinic feldspar, apparently lab- radorite, thus oflFering a transition to diabase. See farther ray researches on euphotide and saussurite ; Silliman's Journal [2] xxvii, 339; and xxxvii, 426. Under the name of dolerite, as already remarked, it is proposed m 20 to class such anonbosite rocks as contain a black ferruginous pyroxene or augite. These rocks, which are sometimes coarsely granular or granitoid in their structure, pass into fine-grained or compact varieties, which are distinguished by the names of anarae- site and basalt. To these latter varieties belong a great part of the greenstone-traps, although in rocks of this texture it is often impossible to determine whether it is hornblende or pyroxene whicli is mingled with the feldspar. Olivine in grains or crystals frequently occurs both in the fine-grained basaltic doleritos and the granitoid varieties, giving rise by its predominance to what is called peridotite. Some fine-grainod dolerites are porphyrilic fiom the presence of black cleavable augite crystals, forming an augite-porphyrv. Finely disseminated carbonates of lime and oxyd of iron are occasionally present in these rocks to the extent of twenty per cent., and even more. In like manner, magnetite and ilmeuite, wbioh are often associated, may constitute several hun- dredths of the mass. Many fine-grainad greenstones contain, like phonolite, large portions oi some zeclilic mineral, and they often abound in chlorite. The pyroxene in these rocks is sometimes replaced by a highly basic silicate. Some varieties of what has been called diallage may be represented as an aluminiferous pyrox- ene "plm a hydrate of magnesia. At other times a mineral approaching in composition to a ferruginous chlorite (frequently amorphous) enters into the composition of these anorthosites,and e>i.n in some cases appears to replace altogether the pyroxene or the hornblende, constituting an aberrant form of diorite or of diabase, which is not uncommon among greenstones, and for which a distinctive name is needed. See on this point Geology of Canada, pp. 469, 605, and the remarks on melaphyiv, below. The finer-graint dolerites are often cellular, giving rise to amygdalo' le, ^hose cavities are generally filled with calcite, quartz, orsonj-3 ^eo'.itic miner-^h. To these amygdaloids tho name of spilitf* fs i«>niatiir.8s gi' n. Earthy varieties of basalt, which are frequently the result of partial decomposition, constitute the wacke of some writers. It is doubtful how far many of thps? spilites and wackes have a claim to be considered as crystallii rocks, inas- much as they appear in very many cases to be nothing more than aqueous sediments accumulated under ordinary conditious, or per- haps in some cases derived from volcanic ash or volcanic mud. As the other extreme of this series of rocks we may notice that dole- I I 21' of rites often assume atrachytio form, —the trachy-dolerites already- mentioned, — or constitute the laras from modern volcanoes. Among the compound rocks which are related to the preceding group by the presence of augi'te, may be noticed nephelinc-dolerite, in which uepheline replaces the feldspar ; and analcimite, a variety into which analcime enters in large amount. Scapolite also in some cases replaces feldspar, and forms with green pyroxene, a peculiar aggregate associated with the Laurentian limestones LGUcite enters as an important element i'i some dolerites, and even replaces wholly the feldspathic element, giving rise to what has befen called leucitophyre or leucilite. [Leucite is generally regarded as an exclusively volcanic mineral ; but according to Fournet, it occurs like other feldspars in rninoral veins, forming the gangue of certain auriferous veins in Mexico (Gdologie Lyonnaise, page 261). According to Scheerer, !<^ufite also occurs in drusy cavities with zeolites and quartz at Arendal in Norway ; although it would seem to be rare in this locality since Durocher was not able to detect it. (Annales desMines[4], i,218). The conditions required for the formation of this feldspathide must be peculiar, since the volcanic rocks which afford it are con- fined to a few localities ; akd since while: it contains a large amount of potash it is a basic silicate, and found among highly basic rocks, in which potash compounds are generally present only in very small quantities. The agalmatolite rocks, including dyssyntribite and parophite (Geology of Canada, page 484), are however basic aluminous silicates in which potash predomioates, and might be supposed under rertaiii conditions of metamorphism to yield leucitic rocks.] Thenameof raelaphyre, which is employed by many writers on lithology requires a rotice in this connection. It was proposed by Brongniart as a synonym for black porphyry (raela-porphyre), and defined by him in 1827 as a porphyry holding crystals of feldspar in a base " of black petrosilicious hornblende." (Classif. des Roches, page 106.) Subsequent researches showed that some of these porphyries were really augitic ; and Von Buch employed the name of melaphyreas synonymous with au^ite-porphyry, in which he was followed by D'Halloy. (Des Roches, p. 15.) In consequence of this confusion, and of the vague manner in which the term is usfifi to include rocks which arp. Rnmstimes slioritss and sometimes varieties of dolerite or basalt, Cotta seems disposed to reject the name of melaphyre as a useless synonym, in which I agree with him. (Gosteinslehre, page 48.) More recently however, Senfi (Die Felsarten, page 263) has endeavored to give a new signification to the term, and defines melaphyre as a reddish-gray or greenish- brown colored rock, passing into black, and containing neither hornblende nor pyroxene. The melaphyres of Thuringia and of the Hartz, according to him, consist of labradorite with iron- chlorite (delessite), carbonates of iron and lime, and a considerable portion of titaniferous magnetic iron. Hornblende and mica arc present only as rare and accidental minerals. We have already alluded to this class of anorthosite rocks, as requiring a distinct- ive name ; but from the historical relations of the word melaphyre. it seems to be an unfortunate appellation for rocks which are not black in color, and from which both hornblende and pyroxene are absent. We now come to consider that third group of silicated rocks, in which the feldspathides arc replaced by the denser double silicates of the grenatide family, garnet, epidote, zoisite, and perhaps ido- crase. Red garnet enters into many gneissic rocks, and even forms with a little admixture of quartz, rock -masses. In some of these, as in the Laurentian series, there appears wi admixture of pyroxene, forming a passage into omphazite or eologite ; which consists of sinaragdite (pyroxene) and red garnet, sometimes mixed with mica, quartz, and kyanite, and passes through an increase of the latter into disthenite or kyanite ro ;k. An agi^regate of horn- blende and red garnet forms beds in the Green Mountains, and an admixture of red garnet with lievrito and a little mica makes up a rock in the Laurentian series. This is evidently related to euly- site, a rock forming strata in gneiss in Sweden, and consisting of garnet, pyroxene, and a mineral 'aving the composition of an olivine in which tlie greater part of the magnesia is replaced by ferrous and raanganous oxyds. Related to this is an apparently undescribed rock from the Tyrol, of which a specimen is before me, consisting of red garnet, green pyroxene, and yellowish-green olivine, the latter greatly predominating; and also a coarsely crystalline rock from Central France, recently described by the name of cameleonite, and composed of olivine, with pyroxeiiu, and onstatite, a magnesian aiigite ; these minerals being accompanied by spinel, splienu, and iliiienite. 1 have already alluded to the true eupbotides, in which a compact zoisite ( jade or saussurite) takes 23 the place of feldspar in a rock the other element of which is pyr- oxene, and have shown how the occasional presence of a triclinic feldspar connects euphotide with diabase. (Silliman's Journal [2], xxvii, 336.) In the same paper are described rocks made up of a white compact girnet with and without hornblende and feld- spar, and also an eftidosite, composed of epidote and quartz. By the disappearance of the aluminous silicate from the rocks of the second and third groups, a passage is established to the am- phibolites and pyroxenites ; and these, through diallage rock, oflfer a transition to the ophiolites or serpentines. These relations are well exhibited in Eastern Canada, where thediorites or greenstones, which are sometimes highly feldspathic, pass into actinolite rock and hornblende slate on the one hand, and into diallagic diabase and diallagic ophiolite on the other. These greenstones, which contain a chloritic mineral, and are often cpidotic, pass gradually into compact or schistose chloritic rocks, fiequently enclosing modules or layers of epidote, either pure ormingl d with quartz. The relations between these various rocks are such that after a prolonged study of them I find it difficult to resist the conclusion that the whole series, from diorites, diallages, and serpentines,to chlorites,epidosites, and steatites, has been formed under similar conditions, ami that they are all indigenous rocks. (Geology of Canada, pp. 606, 6 12, 652.) I have elsewhere express- ed the opinion that these silicates are probably of chemical origin, and li;ive been deposited from solutions at the earth's surface. The sepiolite or hydrous silicate of magnesia, which occurs in beds in tertiary rocks, the neolile of Scheerer, the silicates of lime, magnesia, and iron-oxyd deposited during the evaporation of many natural waters ; and the silicates of alumina likehalloysite, allophane, and eoUyrito, and that deposited by the thermal waters of Plombieres, all show the formation and deposition at the earth's surface of silicates, whose subsequent alteration has probably given rise to many minerals and rocks. (Silliman's Journal [2], xxxii, 286 ; and Cieology of Canada, pp. 659, 577, 581). At the same time the phenomena of local mi^tamorphiKra furnish evidences that similar compounds have resulted from the action of heat upon mechani- cal mixtures in sedimentary deposits. (Ibid., p. 581.) A further consideration of this subject, and of the two-fold origin of many silicious minerals, is reserved for another place. I 24 III. On Some Eruptive Books. In Silliman's Journal for March 1860 (2nd, xxix, 282) there is a short note, pointing out the existence, in the vicinity of Montreal, of several ateresting classes of eruptive rocks, including quartzi- ferous porphyries, trachytes, phonolite, dolerites, and diorites. It is proposed in the third part of the present paper to describe the results of some chemical and mineralogieal examinations of these rocks, and to give by way of preface a description of their geogra- phical distribution and geological relations. They may be con- sidered geographically as belonging to two groups ; of which the first and more important for the number and variety of its rocks may be conveniently described as the Montreal group. It consists of a succession of intrusive masses along a belt running nearly trans- verse to the undulations of the Notre Dame Mountains, which are the prolongation of the Appalachians into eastern Canada. Com- mencing at Shefford Mountain, an isolated trachytio mass not far removed from the western base of the Notre Dame range, we find, going westward, the detached hills known as Yamaska, Kouge' mont, Rouville or Beloeil, Montarville or Boucherville, Mount Boyal or Montreal, and Rigaud Mountains; the last being dis- tant about ninety miles from Shefibrd. Brorae Mountain, which occupies a large area to the south of Shefford, approaches within two miles of it. In like manner, a few miles to the south of Beloeil is another intrusive mass known as Mount Johnson or Monnoir; making in all nine hills of eruptive rock belonging to the Mont- real group. Besides these, numerous smaller intrusive masses in the form of dykes are met with around and between the hills. From Mount Royal to Rigaud Mountain, a distance of about thirty miles, a gentle undulation of the strata is observed, which increases to the westward of Rigaud, and finally gives place to a considerable fault. This disturbance has been traced to the Laurentide hills on the Lac des Chats, 140 miles west of Montreal ; but to the eastward the strata exhibit no evidence of this transverse undulation, unless the ap- pearance of the intrusive rocks already mentioned be supposed to indicate the prolongation of a fracture without sensible dislocation. The whole of these eruptive rocks rise through unaltered paleo- zoic strata, which however, in the immediate vicinity of the intru- give rocks, exhibit a local metamorphism. The hills of Shefford, Brome, and Yamaska break tlirough the strata of the Quebec group, and lie a l-'ttle to the east of the great line of dislocation 25 which, in this region, brings up the lower members of the paleozoic series against the superior portion of the Lower Silurian, and di- vides into two districts the great paleozoic basin, (Geology of Can- ada, pp. 234, 597.) The other hills all belong to the western di- Tiaion of this basin, ?nd break through various members of the Lower Silurian series from the Potsdam to the Hudson River formation. Among the numerous dykes which traverse not only the sedimentary strata but the intrusive masses, there are some which intersect the conglomerates of St. Helen's Island. These are of un- certain age, but repose unconformably on the Lower Silurian series, and enclose pebbles and masses of Upper Silurian limestone charac- terized by fossils of the Lower Helderberg period. (Ibid., p. 356.) This group of intrusive rocks offers very great varieties in com- position ; thus Shefford and Brome consist of what we shall de- scribe as a granitoid trachyte, while the succeeding mountain, Yamaska, and the most western, Rigaud, both consist in part of a kind of trachyte, and in part of diorite. Monnoir and Beloeil also consist of diorites, which however differ from the last two, and from each other; while Rougemont, Montarville, and Mount Royal con- sist in great part of dolerites, presenting however many varieties in composition, and sometimes passing into pyroxenite. The dole- rites of Rougemont and Mount Royal are cut by dykes of tra- chyte. Similar dykes also traverse the diorite of Yamaska, and may perhaps be connected with the trachytic portion of this mountain. It is probable, judging from some specimens from Rougemont, that the dolerite i.; there intersected by veins of diorite, some of which resemble that of Beloeil, and others that of Monnoir. Dykes both of trachyte, phonolite, and dolerite are also found traversing the Lower Silurian strata in the vicinity of the great eruptive masses ; and the conglomerate of St. Helen's mentioned above is traversed by dykes of dolerite, which in their turn arc cut by others of trachyte, A second and smaller group of intrusive rocks occurs to the north- west of Montreal, chiefly in the county of Grenville, where they traverse the gneiss and limestones of the Laurentian system. The principal undulations of these rocks have, like those of the Appa- lachians, a north and south direction ; but there is apparent also a second sCiies of undulations, affecting in a less degree the geo- graphical distribution of the strata, and having, like the Montreal and Rigaud undulation, an east and west diiuction. Coincident with the latter system of folds is a series of doleritic dykes, which nowhere E 26 attain a great breath, but have in some cases been traced more than fifty miles in a nearly east and west direction. These dykes are interrupted by a great mass of reddish syenite, passing in some parts into granite, and occupying an area of about thirty-six square miles in the townships of Grenville, Chatham, and Wentworth. Dykes of this syenite extend from the central mass, and traverse the surrounding gneiss and limestone. Numerous dykes of quartzifer- ous porphyry intersect both this syenite and the surrounding gneiss, and are seen in one case to proceed from a considerable nucleus of porphyry, which rises into a small mountain ; rendering it probable that numerous other porphyry dykes of the region radiate in hke manner from other nuclei of the same rock. Some parts of this porphyry enclose fragments of syenite, dolerite, and gneiss, which vary in size from small grains to several feet in diameter, and often give to the rock the character of a breccia. In one instance a bed of gneiss, upwards of a hundred yards in length, is completely sur- rounded by the porphyry. Orthophyre and Syenite. Orthoclase-Porphyry or Orthophyre.— Under this head may be noticed a rock which has for its base a compact petrosilex, or intimate mixture of orthoclase and quartz, rendered porphyritic by the presence of grains or crystals of orthoclase, of quartz, or of both of these minerals together. The occurrence of this rock at Grenville, where it forms dykes in the syenite of that region, has just been noticed. The fine-grained petrosilicious base of this rock varies in color from dark green to various shades of red, purple, and black ; these differences probably depending upon the degree of oxydation of the contained iron. Throughout this paste are disseminated well-defined crystals of a rose-red or flesh-red feldspar apparently orthoclase, sometimes very abundant; and less frequently small grains of nearly colorless translucent quartz. An analysis was made of a characteristic variety of the rock, the base of which was greenish-black, jasper-like, conchoidal in fracture, and feebly translucent on the edges, with a somewhat waxy lustre. The hardness was nearly equal to thai of quartz, and the specific gravity 2.62. A few distinct crystals of red orthoclase, and some grains of quartz, were present. The base, freed m much as possi- ble from these, gave as follows ; 27 I Silica 72 20 Aluoiina 12.50 Peroxyd of iron 3.70 Lime > 90 Potash 388 Soda 5.30 Volatile 60 99.08 The oxygen ratio of the alkalies and alumina is 2.02 : 5.84, or nearly 1 : 3. The alumina requires 43.80 parts of silica to form with the alkalies 65.48 parts of a feldspar having the ratios 1:3: 12, which are those of orthoclase and albite. There will then remain 28.4 parts of silica. This, with the exception of a small amount which is probably united with the oxyd of iron and lime, way be regarded as uncombined. The porphyries of this region receive a high polish, and are sometimes ve / beautiful. Syenite. — The syenite of this region consists of orthoclase, usually flesh-red in color, and grayish vitreous quartz, with a small portion of blackish-green hornblende, which is sometimes almost or altogether wanting, and is occasionally accompanied with a little mica. The orthoclase is often nearly compact, but more gene- rally distinctly crystalline and cleavable, and so far as observed, is not associated with any triclinic feldspar. The hc.nblende is ap- parently subject to decomposition, becoming soft, earthy, and ferru- ginous in its afpjct, while the feldspar retains its brilliancy. The partial analysis of such a specimen of the syenite gave only 0.56 of lime, and traces of magnesia, with 3.75 per cent, of peroxyd of iron, and of alkalies, potash 4.43, soda 4.35. This large proportion of soda is also to be remarked in the orthophyre just described, and in the red orthoclase-gneiss of this region, a portion of which gave 3.86 per cent of potash and 3.70 of soda ; while the red orthoclase from the rocks of this Laurentian series, named perthite by Dr. Thompson, gives in like manner 6,37 of potash to 5.56 of soda. A nearly pure potash-orthoclase, generally white in color, is how- ever found in some of the stratified Laurentian rocks. (Geology of Canada, page 474.) This syenite of Grenville has in some portions undergone a peculiar decomposition, which has reduced it to a soft greenish matter having the aspect of serpentine, or rather of pyrallolito. This change has been remarked only in the vicinity of some remarkable 28 I veins of chert which are here found cutting the syenite, and as de- scribed by Sir W. E. Logan, is more or less complete for a distance of two hundred yards on each side of them. In specimens of this altered rock, the quartz remains unchanged ; while the feldspar, still preserving its cleavages, has a hardness no greater than car- bonate of lime. It is somewhat unctuous to the touch, with a feeble waxy lustre, and its color is occasionally reddish, but more often of a pale green. Such a specimen was selected for analysis and gave of silica 80.65, alumina 12.60, lime 0.60, soda and a little potash 2.65, volatile 2.10, magnesia and oxydof iron, traces ; — 98.60. From this result it appears that tie feldspar of the syenite has lost nearly two thirds of its alkali ; the iron and other bases having also for the most part disappeared. This removal of the protoxyd bases would appear from the character of the result- ing mineral to be diflFerent from that which takes place during the kaolinization of feldspar. The nature of the process requires further investigation, but it was not improbably connected with the deposition of the adjacent chert or hornstone. This substance, according to Sir W. E. Logan, forms two large veins which cut the syenite vertically, and have a breadth of from four to seven feet. It is generally arranged in bands or layers parallel to the walls of the veins, and varying in color from white to yellowish and flesh- red. The mineral has the chemical characters of flint or buhrstone, and like the latter presents numerous irregular cells, the walls of which are sometimes inorusted with crystals of quartz, and in other cases bear the impression of small cubes, perhaps of crystals of fluor- spar, which have themselves disappeared. The relations of these singular veins of silex show that it cannot be of sedimentary origin, and it can scarcely be doubted that it is an aqueous deposit, and results from a similar process to that which on a lesser scale gives rise to agate and chalcedony in various rocks. (Geology of Canada page 41.) ' Trachytes. Under this head we shall describe a class of rocks which are very abundant in Eastern Canada, and present a great variety of aspects. There are many dykes in the vicinity of Montreal which resemble some of the typical trachytic rocks of Auvergne and of the Rhine; while the rocks of the mountains of Brome and Sliefford consist almost entirely of distinctly crystalline feldspar. These will 29 it ■4 be described as granitoid trachytes, under which head may also be included a somewhat similar rock from Yamaska Mountain. Brome and Shepford Mountains. — The trachytes of Brome and Shefford occupy two considerable areas near to each other and, as already stated, are the easternmost of the eruptive masses now under description. The larger area covers about twenty square miles in Brome and the western part of the township of Shef- ford. It consists of several rounded hills, of which the principal are named Brome and Shefford Mountains, and rise boldly about 1 ,000 feet above the surrounding plain. The rock shows divisional planes, giving it an aspect of stratification, and separates by other joints into rectangular blocks. The second area includes about nine square miles in the township of Shefford, to the northwest of the last, and at the nearest point is only about two miles removed from it. This is known as Shefford Mountain. The rocks of these two mountainous areas present but very slight differences; being, so fur as examined, everywhere made up in great part of a crystalline feldspar, with small portions of brown- ish-black mica, or of black hornblende, which are sometimes asso- ciated. The proportion of these two minerals is never above a few hundredths, and is often less than one hundredth. The other min- eral species are small brilliant crystals of yellowish sphene and others of magnetic iron, amounting together probably to one 'thou- sandth of the mass. In some finer-grained varieties a few rare crystals of sodalite and of nepheline are met with. But for the uniform absence of quartz, these rocks might be taken for varieties of granite and syenite. They are very friable, and subject to disintegration, so that the soil for some distance around these mountains is almost entirely made up of the separated crystals of feldspar; which however show but little tendency to decomposition and retain their lustre. The rock is sometimes rather finely granu- lar in its texture ; but is often composed of clcavable masses of ortho- clase, which are from one fifth to one half of an inch in breadth and son jtimes nearly an inch in length. The lustre is vitreous, and m the more opaque varieties, pearly; but the crystals never exhibit the eminently glassy lustre nor the fissured appearance that characterizes the feldspars of many European trachytes which arc similar to them in composition. The color of the feldspar of l^esc roc_s !s white, pa,?sing into reddish oa the one hand, and into pearl- gray or lavender-gray on the other. I I 30 Specimens of the rock of Brome Mountain were taken from the side near to the village of West Shefford. It was coarsely crys- talline, lavender-gray in color, and contained a little brown mica, sphene, and magnetic iron, but no hombleade. The density of frag- ments of the rock was found to be 2.632-2.638. Selected grains of the feldspar had a specific gravity of 2.575, and gave by analy- sis the result ii. The analysis of a second speoimen from another portica of the hill, is given under ill. The rock from the south side of SheflFord Mountain was next examined. In one part it consisted of a coarsegrained grayish- white feldspar with a little black raica, and closely resembled the rock just described from the adjacent mountain. A little lower down the hill however was a variety which, though completely crystalline, was more coherent and finer-grained than that of Brome, the feldspar rarely exhibiting cleavage-planes more than a fourth of an inch in length. Brilliant crystalline grains of black horn- blende about the size of grains of rice were sparingly disseminated through the mass, together with very small portions of magnetite and yellowish sphene. Fragments of the rock had a density of 2.807- 2.657. The feldspar was yellowish-white and sub-translucent, with a somewhat pearly lustre. By crushing and washing the mass, the grains of feldspar were separated from the heavier minerals, and found to have a specific gravity of 2.561. The result of its anal- ysis, which scarcely differs from that of Brome, is given under iv. II. ni. IV. Silica 65.70 65.30 65.15 Alumina 20.80 20.70 20.55 Lime 84 .84 .73 Potasli 6.43 .... 6.39 Soda 6-52 .... 6.67 Volatile 50 .... .50 100.79 99.99 Yamaska Mountain. — About tweVe miles to the north of west from Shefford Mountain rises the hill of intrusive rock known as Yamaska Mour. tain, which has an area of about foursquare miles, and breaks through the strata of the Quebec group, near *he line of the great dislocatioa which brings these up against the limestones of the Trenton group. The southeastern part of this bill coLsists of a granitoid diorite hereafter to be noticed ; but the greater portion of the mas j may be described as a graaitoid tra- chyte, differing in aspect from that of Brome and Shefford, in 31 being somewhat more micaceoua and more fissile. The mica, which is dark brown, is in elongated flakes, and there is neither horn- blende nor quartz in the specimens collected, which however hold small portions of magnetite, and minute crystals of amber-yellow sphene. These seem to be contained in veins of segregation, which are of a lighter color than the mass. The cleavable feldspar grains, which make up by far the greater part of the rock, are brilliant, with a vitreous lustre, aud are often yellowish or reddish- gray in color. A portion of this feldspar separated by washing from the crushed mass of the rock, had a specific gravity of 2- 563, and gave by analysis the result v. Another portion of selected grains of the feldspar gave vi. Both specimens were however somewhat impure. V. TI. Silica 61.10 58.60 Alumina 20.10 21.60 Peroxyd of iron 2.90 2.88 Lime 3.G5 5.40 Magnesia 79 1.84 Potash 3.54 3.08 Soda , 5.93 6.51 Volatile 40 .80 98.41 99.71 Besides these great trachytic hills, numerous smaller masses of different varieties of trachyte, in the form of dykes and beds, are found along the line of country between Rigaud and Yamaska Mountains. The dioritc of the latter is cut into dykes of a white or Irownish-gray trachyte, which is often porphyritic, and may be connected the great mass just described. Chambly. — At Chambly a mass of porphyritic trachyte is in- truded in t' e form of a bed among the strata of the Hudson Eivc formation ; and about midway in the Chambly canal a simi- lar trachyte is met with, which contains in drusy cavities, crystals of quartz, calcite^ analcime, and chabazite. The base of this rock is of a pale fawn color, and appears at first sight to be micaceous; but on closer examination it is seen to be almost entirely feldsppthie. Minute portions of pyrites, and grains of magnetic iron, are rarely met with, and small scales of a dark green micaceous mineral are very sparsely disseminated. The crystals of orthoclase, which are very abundant, are sometimes an inch in length, and one fourth of an inch in thickness : they are 32 more or less modified, and terminated at both ends. They are easily detached from the rock, and are yellowish and opaque on the exte- rior, but the *ancr portions of the large crystals are transparent and vitreous. The composition of tlie crystals is given undei vil. The paste of this porphyry, when carefully freed from crystals, lost by ignition 2.1 per cent. When pulverized and digested with dilute nitric acid, it eflFervesced slightly, giving off carbonic acid, together with red fumes, arising in part from the oxydation Ox'the pyrites. The portion thus dissolved equalled carbonate of lime 1.76, car- bonate of magnesia 0.98, peroxyd of iron with a trace of alumina 2.12 per cent. The residue, dried at 300° F., gave the result VIII. VII. Tin. Silica 66.15 67.60 Alumina 19.75 18.30 Peroxyd of iron 1.40 Lime 95 .45 Potash 7.53 5.10 Soda 5.19 5.85 Volatile 55 .25 100.12 99.85 The paste of this trachyte thus differs but little from the crys- tals in composition. It contains only a slight excess of silica, and seems to be made up of lamella) of orthoclase, mingled with small portions of cp.rbonates of lime and magnesia. A part of the iron also is probably present as carbonate, which, by its decomposition, gives rise to the rusty red color of the weathered surface of the trachyte. Montreal. — The island of Montreal offers a great variety of trachytic rocks, which traverse both the Lower Silurian strata, and the dolerite of Mount Royal. Some of these dykes are finely granular, occasionally crumbling to sand, and frequently are earthy in texture. In some cases they assume a concretionary structure, and they are often poiphyritio from the presence of feldspar or hornblende. One variety exhibits large feldspar crystals in a is ig given under ix; while that of the matters dissolved by nitric acid 34 and carbonate of soda from 100 parts of the rock, will be found under ix A. A dyke of trachyte near to the last, and very similnir to it in appearance, was submitted to the action of nitric acid, but the in- soluble residue was not treated by carbonate of soda. Its analysis is given under x, while that of the soluble matters is to be found under x a. A white trachyte from a dyke at Lachine, resembled the preceding, but was somewhat earthy in its aspect, and eflFer- vesced with nitric acid, which removed a portion of lime equal to 7.40 per cent of carbonate. On boiling tLe pulverized rock with nitrate of ammonia, an amount of lime equal to 5.33 per cent of carbona*^ was dissolved. An accident prevented the complete deter- mination of the alkalies in the feldspathic residue of this trachyte ; and the soluble silica was not removed previous to the analysis, whose result is given under xi. The proportion of the potash to the soda was however found to be, by weight, nearly as two to three. The matters dissolved by nitri: acid will be found under XI A. Another dyke of trachyte from Lachine was concretionary, and stained by infiltration ; the interior of the concretions was white and earthy. The substances removed from 100 parts of the rock by nitric acid and carbonate of soda, are given under E. A par- tial analysis of the insoluble residue shovvcd it to be a feldspar aUied to th ^e of the preceding trachytes : the quantities of potash and soda were however nearly in the re ';-o of four to three. A large dyke of trachyte in the limestone quarries at the Mile End, near Montreal, is remarkable for the amount of carbonates which it contains. It is grayish-white, with dark grey spots, gran- ular, sub-vitrcous in lustre, and holds a few crystals of hornblende. By ignition it loses 11.0 per cent, of its weight. In powder it effervesces freely with nitric acid, disengaging carbonic acid, and when hfiat is appHed, red fumes from the peroxydation of the iron. 100 parts of the rock yielded in this way the soluble matters given under xii a. The composition of the residue, from which the soluble silica was not removed, is given under Xil. IX. X. XI. XII, «j:,j^^„ 63.25 62.90 58.50 61.62 Al'umina,'.*.'.'.' 22.12 23.10 24.90 21.00 Lime 56 .45 .45 2.69 Potash 5,92 2.43 ,..- 4.66 Soda 6.29 8.69 .... 5.35 Volatile __93 _^40_ J^ _Jfl 99.07 98.37 ^''•69 85 A second determination of the alkalies in a portion of the tra- Chyte IX, which had not previously been treated by acid, gave potash 5.40 and soda 6.49. A second analysis of x gave potwh 2.28, and soda 7-95. ,o„. "*• »A. JCIA. B. XII A. ^"••'* 1-43 5.00 .... "^*°™'°'' 2.43 .... 1.27 1.32 4.84 Peroxydofiroa 2.40 2.84 1.47 2.51 2.63 f;™*" 60 1.86 4.14 3.50 6.49 ^"K""^'* 1.34 1.35 1.70 f"*"^''' 40 .25 undet. undet. undet »o -i of carbonate of soda, 9 5 per cent of its weight oi' soluble .silica : and the insoluble portion, being sub- 1) 50 mitted to analysis, gave the result i. A portion of the limestone which was near to the intrusive rock, and had become hardened and partially altered, was subjected to the action of dilute nitric acid, and gave an insoluble residue with the composition ii. The more thoroughly altered greenish limestone was also treated with dilute nitric acid, which dissolved the carbonate of lime, and left a resi- due, the analyses of which, from two different portions of the rock, are eiven under iii and iv. *= I. H. III. IV. ailica, 73.02 54.00 42.00 40.20 Alumlni; *'.'■.'/.'.'. 1«-31 14-00 13.70 9.30 Lime 93 1G.24 31.