gible to the initiated. However, an examination of those off-spurs and boulders which lie nearest the town, has led those who understand the subject to infer, that granite, granitic gneiss, mica slate, (rarely), syenite, syenitic gneiss, horneblende slate, and primary greenstone, are the species of rocks which most prevail. Transition Rocks. The term Transition in Geology, is becoming obsolete; yet it is one of great convenience, and liable to no abuse when employed by those who study facts more than theories. We will, therefore, continue to employ it in the designation of certain rocks which are largely developed in the immediate neighbourhood of Quebec, and on one or two members of which, indeed, we consider that City to stand. When placed on the highest summit of Cape Diamond, 350 feet above the river at its base, all the natural stony fixed features of ground around and beneath us on this side the valley of the St. Charles and on the opposite side of the St. Lawrence, consist of Transition rocks.-This formation characterizes both shores of the St. Lawrence for some distance above Quebec; but below it appears to be, for the most part, confined to the islands and southern shore, which it exclusively occupies for many miles. The members which compose this formation, in the extent to which we now limit our attention, are the following:-Clay slate, greywacke, compact limestone and limestone conglomerate: the two first occur in very subordinate quantity, while the two former abound and frequently alternate with each other. The dip of the stratification of these rocks, which shows this alternation, is usually at a high angle to the S. E.; but occasionally the reverse of this dip is noticed, and the inclined planes of the strata front the N. W., the bearing of N. E., S. W. remaining generally undisturbed. Cape Diamond, in which this formation attains its greatest height, at least in the neighbourhood of Quebec, consists of a clay slate, but of anomalous constituents, among which are to be reckoned a large portion of carbonate of lime, carbon and bitumen;" and in consequence, the rock has been called a carboniferous limestone by those who attend more to the mineralogical than geological character; forgetting at the same time, that the term carboniferous, implies bearing carbon, not containing it, the carboniferous being the lowest rock of the coal formation. We must not omit to state, however, that it is a question of controversy with Geologists, whether carboniferous limestone be the lowest of the Secondary or uppermost of the Transition class.-Be this at it may, the dip of the rock in question, conformable to that of the series in the vicinity, of decided Transition character, together with the rarity (to say the most) of the occurrence of fossils in it, corresponds so well with the Transition class around, while these characters are so perfectly at variance with those of the horizontal fossil bearing† strata of Beauport, which is * The abundance of quartz crystals also with which it is studded, and to the presence of which it owes its name, may be likewise considered as an anomalous characteristic. We do not know of any positive instance of the occurrence of fossils in the Black Rock of Quebec; but bivalvular impressions have sometimes (though rarely) been noticed in the conforma really conceived to be carboniferous limestone, that we have no hesitation in claiming for the former, both a higher degree of geological antiquity and a distinct geological epoch. Secondary Rocks. The Secondary rocks of the vicinity next come under consideration: they consist, almost exclusively, as far as we have yet noticed, of a limestone which is fetid, fossilized and horizontally stratified, holding a position topographically between the Primary range to the northward, and the Transition masses we have just alluded to on the opposite or St. Lawrence side of the valley, while their relative geological arrangement is either over the edges of the highly inclined clay slates or grey wackes, or where they basset out, abutting against the planes of their stratification, or, when these rocks are absent, coming into similar contact with the primary stratified formations beneath, or simple contact alone, either vertically or laterally, with the unstratified portion of the same in short, always in a position relatively unconformable to those rocks we have stated to represent the Primary and Transition classes of the neighbourhood. The localities which offer the best sections of the limestone we are discussing, are, the village of Beau ble limestone conglomerates which form the northern precipice, from the corner of Peter-street towards No. 4 Tower. It is worthy of remark, that the planes of stratification of the Black Rock often exhibit continuous markings, analogous to trellis work, which have a high relief, as well as a anthracitic lustre. It has just been discovered that this rock forms by the usual process, an excellent water cement, &c. port and the Montmorenci river; the former an artificial quarry, the latter, we conceive, the result of a natural watery erosion. Both these sections have been closely examined by Dr. Bigsby, who has the credit of having been one of the first individuals in this country to stir up a taste for similar investigations; and we cannot do better than introduce here an extract of his, taken from Professor Silliman's "Tour between Hartford and Quebec," the only tour published among the many through this place which affords accurate geological information on the locale, and which, in other respects, is a work so pleasantly (and as far as we may presume to judge correctly) written-breathing throughout such a tone of conciliation as to enlist the sympathies of the reader in its behalf, whether he be American or British, while it tends to his conviction that the author is, not only a scholar, but also a liberal minded gentleman : "The lowest visible rocks, rising six or eight feet from the bed of the river, are dough shaped mounds of granite, (gneiss?) vertical, with a south-west direction, with many irregular quartz veins, half a foot thick. On it, lies a perfectly horizontal sand stone, so coarse as to resemble conglomerate, (I suspect this sand stone is a coarse gray wacke.) It is four feet thick, and weathered red and white. Upon this rests light hair brown, highly crystalline lime stone, very fetid, full of shells, vegetable filaments, massive blende, and a mineral, like brown spar. This gradually becomes dull, less crystalline, and at length at the top of the bank, is nearly a common blue lime stone, with a conchoidal fracture, and still here and there containing small crystals of carbonates. The whole height here, is perhaps, forty feet." About one mile above the place of which the foregoing extract is a geological description, occurs a gorge or deep section in the river which, from the step-like placement of portions of the horizontal strata form.ng its sides, has been called, appropriately, "The Natural Steps." Here is met with a very interesting geological section, consisting of a succession of horizontal strata of fetid limestone, filled with the "Medals of Creation," as fossils have been eloquently called, the most abundant among which are othoceratites. Near the base of this section, a little above the river, a thin stratum may be noticed, which is literally composed of ammonites about there or four inches in circumference; some of them very perfect and beautiful. This stratum is pressed by a superincumbent mass of limestone, of from 30 to 40 feet high. Both banks of the river here exhibit much the same appearances, being characterized by the same fossils and limestone. Among other fossils characteristic of the carboniferous limestone met with in this formation, both here and at Beauport, are certain corallites, trilobites, encrinites productæ, terbratulæ, conulariæ quadrisulcatæ, (rare), and nautulites. * Tertiary-Alluvial-Diluvial Formations. We class all these hydraulic deposits together, because, in fact, with one exception, it is in general *Art. 9, vol. 1. Transactions of the Literary and Historical Society of Quebec, affords good Topographical and Geological Notes on the country in the neighbourhood of the Falls of Montmorenci. |