i6o Transactions of the Canadian Institlte. [Vol. VII. 



readily friable and forms a beach of small gravel just at the foot of the 

 cliff. The constituents of this arkose are distinctly different from those 

 of the adjacent gneiss. The nearest outcrop of gneiss is one hundred 

 yards away, and the water between reaches a maximum depth of nine 

 feet, but, from the conformation of the bottom, the exposed portion of the 

 deposits must evidently be within a very few feet of the gneiss imme- 

 diately below it. The deposits may be regarded as a remnant of the 

 old soil cover of pre-sedimentary times, slightly rearranged. 



Black River and Later Formations. — Succeeding these 

 unidentified beds are the Black River limestones, which form a cuesta, 

 whose northern boundary forms an escarpment extending from 

 Georgian Bay to Kingston. The Black River beds are succeeded by 

 the Trenton limestones with a thickness, as calculated from the dips near 

 the eastern end across Prince Edward county, of over 1,400 feet. These 

 are overlain by about 100 feet of Utica shales. Above this are nearly 

 800 feet of Lorraine shales and sandstones, overlaid in turn by 545 feet of 

 Medina marls and sandstones. The upper bed of the Medina is, in 

 Central Ontario, a heavy gray sandstone, about twelve feet in thickness, 

 but occasionally thicker. The beds above this, found in the Niagara 

 escarpment, consist of Clinton dolomitic limestones and shales, overlaid 

 by the Niagara limestone. Throughout the region, so far as known, 

 there is no observed unconformity between the beds of the various 

 formations. 



Summary of the Pal.^ozoic History. — The geologic history 

 of the area, subsequent to the period of denudation and dissection of 

 the crystallines, was begun by a depression of the land, during which some 

 small amounts of sand were deposited along and near the shores, with 

 deposits which formed shales and limestones in the deeper waters. 

 This depression continued somewhat faster than the rate of supply of 

 detritus, and finally limestones, which, however, contain siliceous 

 material, were deposited over the whole area. The waters were " richly 

 tenanted by a great variety of forms of invertebrate life, and repre- 

 senting the culmination of invertebrate animals in the Lower Palaeozoic" 

 (Dawson, '89, 73). The great thickness of the deposits indicates that 

 the Trenton epoch was of considerable duration. Towards the close of 

 the limestone-forming epoch a variation took place, the new material 

 supplied to this area was in the form of clays and muds. The change 

 in the character of the deposits was accompanied by a change in the 

 types of animal life here present. This change, marked by the Utica 

 shales, was probably caused in part b\' a decrease in the rate of depres- 



