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These shells imply a higher beach than that of this lower flat, which is not more than 30 feet above the present sea level. Accordingly above this are several higher terraces, the heights of which on the west side of bay are given in Section I. The second principal terrace, which forms a steep bank of clay some distance behind the main road, is 116 feet in height, and is of considerable breadth, and has on its front in some places an im. perfect terrace at the height of 81 feet. It corresponds nearly in height with the shoulder over which the road from the pier passes. Upon it, in the rear of the property of Mr. Du Berger, is a little stream which disappears under ground, probably in a fissure of the underlying limestone, and returns to the surface only on the shore of the bay. Above this is a smaller and less distinct terrace 139 feet high. Beyond this the ground rises in a steep slope, which in many places consists of calcareous beds, worn and abraded by the waves, but showing no distinct terrace ; and the highest distinct shore mark which I observed, is a narrow beach of rounded pebbles at the height of more than 300 feet; but above this there is a flat at the height of 448 feet. This beach appears to become a wide terrace further to the North, and also on the opposite side of the bay. It probably corresponds with the highest terrace observed by Sir W. E. Logan, at Bay St. Paul, and estimated by him at the height of 360 feet.
As already stated, three of the principal terraces at Murray Bay correspond nearly with three of the principal shore levels at Montreal; and in various parts of Canada, two principal lines of old sea beaches occur at about 100 to 150 feet, and 300 to 350 feet above the sea, though there are others at different levels.
In the Post-pliocene period the valley of the Murray Bay river has been filled, almost or quite to the level of the highest terrace, with an enormously thick mass of mud and boulders, washed from the land and deposited in the sea bed during the long period of Post-pliocene submergence. Through this mass the deep val. ley of the river has been cut, and the clay, deprived of support and resting on inclined surfaces, has slipped downward, forming strangely shaped slopes, and outlying masses, that have in some instances been moulded by the receding waves, or by the subsequent action of the weather, into conical mounds, so regular that it is difficult to convince many of the visitors to the bay that they are not artificial. Sir W. E. Logan iv his report on the district has in my view given the true explanation of these mounds, which may be seen in all stages of formation on the neighbouring hill sides. Their effect to a geological eye is to give to this beautiful valley an unfinished aspect, as if the time elapsed since its elevation had not been sufficient to allow its slopes to attain to their fully rounded contour. This appearance is no doubt due to the enormous thickness of the deposit of Post-pliocene mud, to the uneven surfaces of the underlying rock, and possibly also in part to the earthquake shocks which have visited this region.
At the mouth of the Murray Bay River, the Boulder-clay, which rests directly on the striated rock surfaces, and which is a true till, filled with the Laurentian stones and boulders of the inland hills, though resting on Silurian limestone, is evidently marine, since it contains shells of Leda truncata ; and many of the stones are coated with Bryozoa and Spirorbes. It is also observable that on the N.E. sides of the limestone ridges the boulders are more numerous and larger. Above the Boulder-clay may in some places be seen a stratified sandy clay, which further up the river attains to a great thickness. It contains Saxicava rugosa, Tellina Grænlandica, and Tellina calcareu, as well as Leda truncata. The most recent deposit is a sand or gravel, often of considerable thickness, and in some of the beds of gravel the pebbles are more completely rounded than those of the modern beach.
I have already, in Section I, stated my reasons for believing that the upper part of the valley of the Murray Bay River may have been the bed of a glacier flowing down from the inland bills toward the St. Lawrence. N.W. and S.E. striæ attributable to this glacier were seen at an elevation of 800 feet, and the marine beds were traced up to almost the same height, above which, to a height of about 1200 feet, loose boulders were observed and glaciated rock surfaces, but no marine deposits. It is probable, therefore, that at a time when the sea extended up to an elevation of 800 feet, the higher part of the valley may have been filled with land ice. Whether the bergs from this, drifting down toward the St. Lawrence, produced the N.W. striation observed at a lower level, or whether at a previous period, when the land was higher, the ice extended farther down, may admit of doubt. Certainly no land ice has extended to a lower level than about 800 feet, since the deposition of the marine boulder and Leda clay.
Very large boulders occur in this vicinity. One observed on the beach on the east side of the Bay, is an oval mass of lime felspar, thirty feet in circumference, lying like most other large boulders in this region, with its longer axis to the N.E.
Les Eboulements.—At this place the Laurentian hills rise to a great height near the shore, and the Post pliocene beds present the exceptional feature of resting on soft decomposed Silurian shale (Utica shale). This rock might indeed be mistaken for drift, but for its stratification, and it inust have been decomposed to a great depth by subaerial action and subsequently submerged and covered by the Post-pliocene beds. Its preservation is the more remarkable that the clay overlying it contains very large Laurentian boulders, which must have been quietly deposited by floating ice. Only a few shells of Tellina Greenlandica were observed in these clays.
The remarkable series of terraces seen at this place, and noticed in part first, rising to 900 feet in height, are all cut out of the Post-pliocene beds and decomposed shale, and even the highest presents large boulders. In examining such terraces it is always necessary to distinguish between the clays out of which the terraces have been cut and the more modern deposits resting on the terraces. Both may contain fossils, but those of the original clay are in this region mostly of deeper water species than those in the overlying superficial beds.
I attribute the preservation of the thick beds of Boulder-clay and the decomposed shale at Les Eboulements, to the fact that no transverse valley exists here, and that a point of high Laurentian land projects to the North-East, so as to shelter this place from forces acting in that direction. I have observed this appearance on the lee or South-west side of other projecting masses of hard rock, and as the decomposed shale must be a monument remaining from the Pliocene elevation of the land, it shews that no powerful eroding force had acted between that time and the period of the N. E. arctic ice-laden currents.
It is perhaps deserving of notice that the thick beds of soft material at Les Eboulements have been cut into many irregular forms by modern subærial causes of denudation, and also by landslips, which last have been in part connected with the earthquake shocks with which this part of the coast has been visited more than
other district of Canada. Above Les Eboulements, Bay St. Paul presents features similar to those of Murray Bay, and then the Laurentian land of Cape Tourment comes boldly forward to the shore of the River. Above this the conditions are similar to those observed in the neighbourhood of Quebec.
(To be continued.)
ON THE “COLONIES” OF M. BARRANDE.
By HENRY ALLKYNE Nicholson, M.D., D.Sc., M.A., Ph.D., F.R.S E.,
F.G.S., &c. Professor of Natural History and Botany in University College, Toronto.
The doctrine of " Colonies," propounded by M. Barrande, has been long before the palæontological world, and is known, at any rate by name, to all students of geology. It is doubtful, however, if there is as clear a comprehension of this subject as its importance would render desirable; and it may, therefore, be of interest to discuss briefly the leading facts upon which this theory is based. In so doing, I shall take the necessary details from M. Barrande's “Défense des Colonies," published in 1870, one of the most valuable of the many palæontological works of this distinguished observer, and I shall confine myself chiefly to a resumé of the facts therein recorded and the deductions drawn therefrom.
I. SUB-DIVISIONS OF THE Silurian Rocks OF BOHEMIA.
The Silurian Rocks of Bohemia are described by M. Barrande as occupying an elliptical basin, the long axis of which has a N.E., and S.W. direction, and a length of 148 kilometres. The breadth of the basin increases gradually in passing from the N.E. to the S.W., its minimum breadth being about 30 kilometres, and its maximum about 74 kilometres. The Silurians of this basin repose upon granitic and gneissic rocks, and dip inwards towards a central line. The fossiliferous beds of the entire basin occupy a far fron considerable superficial area; and their extent -supposing them not to have been much denuded—would assign to the Silurian sea of Bohemia an area not exceeding 1-60 of the superficies of the Adriatic.
The Silurian rocks of the entire basin admit of separation into two primary divisions, an Inferior and a Superior division, corresponding respectively to the Lower and Upper Silurian Rocks of Sir Roderick Murchison. The Inferior Division is composed principally of schists and quartzites; or, as we should say, slates and grits or graywackes, and is wholly destitute of calcareous
matter, except occasional concretions of carbonate of lime. The Superior Division is composed almost entirely of calcareous matter, with merely subordinate bands of schists and quartzites. Each division can be satisfactorily broken up into four sub-divisions (étages), grounded solely upon the characters of their contained fossils, and lettered in ascending order :
The étages of the Inferior Division are A., B., C., D. The étages of the Superior Division are E., F., G., H. Each of the fossiliferous sub-divisions can be further broken up into minor groups or “bands," distinguished by the smaller letters of the alphabet, as shown in the annexed table.
Etages A. & B., the lowest of the Inferior Division, are composed of semi-crystalline rocks and conglomerates, and are unfossiliferous. They are termed by Barrande the “ Azoic Etages," and are considered by himn as forming the base of the Silurian Series. It is, however, more probable that they should be regarded as being truly of Lower Cambrian age.
Etages C. D. E. F. G. & H. are fossiliferous. Etage C. is the well-known “ Primordial Zone ” of Bohemia, corresponding with the Menevian beds of Britain, and characterized by primordial trilobites of the genera Parado.cides, Olenus, Conocoryphe, Ellip tocephalus, &c. It should probably be regarded as Upper Cambrian.
Etage D. contains Barrande's so-called “ faune second' second fauna, and must correspond with the Llandeilo and Caradoc beds of Britain. Etages E. F. G. & H. are characterized by a single fauna termed by Barrande the “faune troisième" or third fauna; and they correspond collectively to the Upper Silurian Rocks of Britain.
The precursors (“ avanteureurs ") of this “third fauna” in the last portions of the period of the “second fauna” are termed by Barrande the “colonies." They are in the form of bands which are enclosed in the mass of étage D towards its higher part, and which are thus stratigraphically Lower Silurian, but which, nevertheless, contain a predominance of fossils characteristic of the "third fauna," and thus come paleontologically to belong to the Upper Silurian series. They abound especially in the band d 5, occurring also in d 4, and about twenty of them are known in all. The subjoined table shows in a summary form the general subdivisions and lithology of the rocks of the Bohemian basin, with the principal characteristic fossils :