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of iron, having evidently suggested the name by which the promontory is known. The latter, as stated in a preceding paragraph, marks the southern limit of the metamorphic belt, the contact of this with the Mesozoic traps being well exposed in a small cove upon its western side. The red slates last described, dipping northward, here meet and are covered by a coarse conglomerate made of dark trap pebbles, which in turn underlies and passes into coarsely columnar trap, these being the first of a succession of such beds forming the northern shore of Benson's Cove.

Several small groups of islands lie to the south and east of the promontory last described. These I have only partially examined, but as they exhibit some features not met with upon the mainland, they may be briefly alluded to here. The first of these groups is that known as the Wood Islands, distinguished as the Inner and Outer Wood Islands. Upon the former the rocks bear much resemblance to those seen along the western side of Grand Harbour, described above. They are rather fine grained rocks, of bright green, red, and purple colours, often diversified with paler bands and blotches, and more or less filled with amygdules of calcite and epidote. These beds are associated with sandstones (and some conglomerates) of deep red and purplish red colours, sometimes finely banded and alternating with thinner beds of pale grey feldspathic schist and impure dolomite. These rocks, with occasional masses of trap, form nearly the whole of the western side of the island, as well as its northern extremity, their dip being somewhat variable, but where most regular, about N. 20 to 60° E. > 40°. The sandstones are at some points very curiously and conspicuously marked by narrow veins (one-fourth of an inch wide) of fibrous calcite or satin spar, which fill short lenticular cavities arranged in parallel and overlapping lines, at right angles to the bedding of the rock.

Outer Wood Island, at the only point seen by me (on its eastern side), is composed of hard greenish-grey silico feldspathic rocks, with very obscure stratification.

The group of the Three Islands lies to the south and east of that last described, and with the exception of Gannet Rock, on which a light-house is built, is the most southerly of the chain of islands about the entrance of the Bay of Fundy. On the larger island of this group, known as Kent's Island, are beds of crystalline limestone. They are mostly light coloured but mottled with shades of green, grey, or pink, and are rendered impure by a

considerable admixture of quartz. The associated rocks are pale grey light weathering feldspathic grits, somewhat granitoid. in aspect, grey feldspathic quartzites, and greenish and purplish. altered schists, all much broken and disturbed. The other islands in this group I have not examined.

With reference to the age of the metamorphic rocks described above, I can only add to the various conjectures already made by other authors. In doing so, however, I may say that I have had the advantage of being able to compare them directly with the formations of the mainland, and thus of arriving at a more probable estimate of their true position than is likely to be obtained from the mere study of the rocks themselves. Of the recognized formations in New Brunswick, they bear no resemblance to either the Laurentian, Primordial, Upper Silurian, or Carboniferous. They are equally unlike the Devonian rocks, so far as these have been clearly determined on palæontological evidence. They do, however, bear much resemblance to an assemblage of strata met with at various points along the southern coast of the Province as well as in the interior, and to a portion of which a Devonian age has been assigned in earlier publications. The rocks in question, embracing like those of Grand Manan a series of coarse red sediments, grey clay slates, chloritic slates and grits, with some limestones and dolomites, were at some points found to rest upon undoubted Devonian beds, and were for this reason referred to that horizon. It is not yet certain that such is not their age, but a careful study of the district having shewn the existence therein of several great faults and overlaps, it is possible that the beds in question, notwithstanding the superposition referred to, are really much more ancient. If this is the case, there can be no doubt that they are to be looked upon as a subordinate division of the great Huronian series, to the other members of which, as recognized in southern New Brunswick, they bear much resemblance. The metamorphic rocks of Grand. Manan have been compared by Dr. Dawson (from Prof. Verrill's description) with what has been termed the Kingston series on the mainland of the Province. They differ from these latter in some respects, but as these Kingston rocks are now also believed to be a subdivision of the Huronian system, (and not Upper Silurian, as at one time supposed) this comparison may be taken as an additional argument in support of the view here advocated. Prof. Verrill has suggested that possibly more than one group

may be represented among the metamorphic rocks of Grand Manan. I also incline to this opinion (more particularly as regards the strata first described between Whale Cove and Pette's Cove as compared with those on the coast and islands southward of the latter,) but think that neither will be found to be more recent than the earliest Primordial Silurian.

The accompanying map is a copy of the Admiralty chart of Grand Manan, slightly modified to show the position and extent of its geological formations.

ON THE OIL-BEARING LIMESTONE OF CHICAGO.

BY T. STERRY HUNT, LL.D., F.R.S.

(Read before the American Association for the Advancement of Science, at Troy, August, 1870.)

When in 1861,* I first published my views on the petroleum. of the West, I expressed the opinion that the true source of it was to be looked for in certain limestone formations which had

long been known to be oleiferous. I referred to the early observations of Eaton and Hall on the petroleum of the Niagara limestone, to numerous instances of the occurrence of this substance in the Trenton and Corniferous formations and, in Gaspé, in limestones of Lower Helderberg age. Subsequently, in this Journal for March, 1863, and in the Geology of Canada, I insisted still farther upon the oleiferous character of the Corniferous limestone in south-western Ontario, which appears to be the source of the petroleum found in that region. I may here be permitted to recapitulate some of my reasons for concluding that petroleum is indigenous to these limestones, and for rejecting the contrary opinion, held by some geologists, that its occurrence in them is due to infiltration, and that its origin is to be sought in an unexplained process of distillation from pyroschists or so-called bituminous shales. These occur at three distinct horizons in the New York system, and are known as the Utica slate, immediately above the Trenton limestone, and the Marcellus and Genesee slates which lie above and below the Hamilton shales, the latter being separated from the underlying Corniferous limestone by the Marcellus slate.

• Montreal Gazette, March 1, and this Journal, July, 1861.

First, these various pyroschists do not, except in rare instances, contain any petroleum or other form of bitumen. Their capability of yielding volatile liquid hydrocarbons or pyrogenous oils, allied in composition to petroleum, by what is known to chemists as destructive distillation, at elevated temperatures, is a property which they possess in common with wood, peat, lignite, coal, and most substances of organic origin, and has led to their being called bituminous, although they are not in any proper sense bituminiferous. The distinction is one which will at once be obvious to all those who are familiar with chemistry, and who know that pyroschists are argillaceous rocks containing in a state of admixture a brownish insoluble and infusible hydrocarbonaceous matter, allied to lignite or to coal.*

Second, the pyroschists of these different formations do not, so far as known, in any part of their geological distribution, whether exposed at the surface or brought up by borings from depths of many hundred feet, present any evidence of having been submitted to the temperature required for the generation of volatile hydrocarbons. On the contrary they still retain the property of yielding such products when exposed to a sufficient heat, at the same time undergoing a charring process by which their brown colour is changed to black. In other words these pyroschists have not yet undergone the process of destructive distillation.

Third, the conditions which the oil occurs in the limestones, are inconsistent with the notion that it has been introduced into these rocks by distillation. The only probable or conceivable source of heat, in the circumstances, being from beneath, the process of distillation would naturally be one of ascension, the more so as the pores of the underlying strata would be filled with water. Such being the case, the petroleum of the Upper Silurian and Lower Devonian limestones must have been derived from the Utica slate beneath. This rock, however, is ualtered, and moreover, the intermediate sandstones and shales of the Loraine, Medina and Clinton formations, are destitute of petroleum, which must, on this hypothesis, have passed through all these strata to condense in the Niagara and Corniferous limestones. More than this, the Trenton limestone which, on Lake Huron and elsewhere, has yielded considerable quantities of petroleum, has no pyroschists beneath it, but on Lake Huron rests on ancient crystalline rocks,

• Silliman's Journal, II, xxxv, 159-161.

with the intervention only of a sterile sandstone. The rock-formations holding petroleum are not only separated from each other by great thicknesses of porous strata destitute of it, but the distribution of this substance is still farther localized, as I many years since pointed out. The petroleum is in fact in many cases, confined to certain bands or layers in the limestone, in which it fills the pores and the cavities of fossil shells and corals, while other portions of the limestone, both above, below, and in the prolongation of the same stratum, though equally porous, contain no petroleum. From all these facts the only reasonable conclusion seems to me to be that the petroleum, or rather the materials from which it has been formed, existed in these limestone rocks from the time of their first deposition. The view which I put forward in 1861, that petroleum and similar bitumen have resulted ftom a peculiar "transformation of vegetable matters, or in some cases of animal tissues analogous to those in composition," has received additional support from the observations of Lesley,* in West Virginia and Kentucky, and from the more recent ones of Peckham.†

The objection to this view of the origin and geological relations of petroleum, have been for the most part founded on incorrect notions of the geological structure of southwestern Ontario, which has afforded me peculiar facilities for studying the question. In this region, it has been maintained by Winchell that the source of the petroleum is to be sought in the Devonian pyroschists. I however showed in 1866, as the result of careful studies of the various borings: first, that none of the oil-wells were sunk in the Genesee slates, but along denuded anticlinals where these rocks have disappeared, and where, except the thin layer of Marcellus slate sometimes met with at the base of the Hamilton shales, no pyroschists are found above the Trenton limestone. Second, that the reservoirs of petroleum in the wells sunk into the Hamilton shales are sometimes met with in this formation, and sometimes, in adjacent borings, only in the underlying Corniferous. Examples of this have been cited by me in wells in Enniskillen, Bothwell, Chatham, and Thamesville, where petroleum has first been found at depths of from thirty to one hundred and twenty feet in the

Rep. Geol. Canada, 1866, 240; and Proc. Amer. Philos. Soc. x, 33, 187.

† Ibid, x, 445.

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