In this district, and the eastern part of North America generally, it is, I think, universally admitted that the later Pliocene period was one of continental elevation, and probably of temperate climate. The evidence of this is too well known to require re-statement here. It is also evident, from the raised beaches holding marine shells, extending to elevations of 600 feet, and from drift boulders reaching to a far greater height, that extensive submergence occurred in the middle and later Pleistocene. This was the age of the beds I have named the _Leda_ clays and _Saxicava_ sands, found at heights of 600 feet above the sea in the St. Lawrence valley, nearly as far west as Lake Ontario. It is reasonable to conclude that the till or boulder clay, under the Leda clay, belongs to the earliest period of probably gradual subsidence, accompanied with a severe climate, and with snow and glaciers on all the higher grounds, sending glaciated stones into the sea. This deduction agrees with the marine shells, polyzoa, and cirripedes found in the boulder deposits on the lower St. Lawrence, with the unoxidized character of the mass, which proves subaqueous deposition, with the fact that it contains soft boulders, which would have crumbled if exposed to the air, with its limitation to the lower levels and absence on the hillsides, and with the prevalent direction of striation and boulder drift from the north-east.[167] [167] Notes on the Post-Pliocene _Canadian Naturalist_, _op. cit._; also Paper by the author on Boulder Drift at Metis, _Canadian Record of Science_, vol. ii., 1886, p. 36, _et seq._ All these indications coincide with the conditions of the modern boulder drift on the lower St. Lawrence and in the Arctic regions, where the great belts and ridges of boulders accumulated by the coast ice would, if the coast were sinking, climb upward and be filled in with mud, forming a continuous sheet of boulder deposit similar to that which has accumulated and is accumulating on the shores of Smith's Sound and elsewhere in the Arctic, and which, like the older boulder clay, is known to contain both marine shells and driftwood.[168] [168] For references see "Royal Society's Arctic Manual," London, 1875, _op. cit._