GEOLOGY The Pleistocene age, in which flourished several forms of mammalia some of which are now extinct, together with the subsequent interval, make up the Quaternary period. By far the larger portion of the Quaternary deposits has been spread out on the submarine shelf that fringes the coast, a tract which the mutability of events may eventually convert into a future land surface. The preceding Tertiary period, by reason of its greater antiquity, has been subjected to a far longer experience of crustal oscillation, in which sufficient time has been afforded for those more ancient accumulations, together with such portions of the submarine shelf on which they were deposited, to be gradually upheaved ; so that a considerable area of the Cornish platform of to-day marks the site of the bed of the Tertiary seas, while the few marine accumulations of those seas that have survived the long period of denudation since their emergence from the ocean floor, yield unequivocal testimony to the vast changes in the past in which the boundaries of land and sea have taken part. The rigorous conditions of the glacial epoch were preceded by periods of subtropical climate, which characterized the Miocene age. The interval between these two extremes, in which climatal conditions represented a temperate zone, constitutes the Pliocene period, the youngest division of the Tertiary strata. Although these deposits present a very general resemblance to the beds at present being formed on our littoral, the shells which they enclose are not confined to species that now inhabit our seas, but include forms which at the present time find their habitat in the more northern and more southern seas. Not only do the fossil remains reflect the transitional conditions which connected the climatal extremes already alluded to, but a large proportion of the species which flourished in the Pliocene seas have become extinct. The only deposits in Cornwall which can with certainty be referred to the Pliocene period occur in the neighbourhood of St. Erth, occupying a very small area, and probably owe their preservation to the protection afforded them by their physical situation. The discovery of this small relic of the Pliocene shelf is very recent, and was brought about by the deepening of a clay pit which revealed shells in the subjacent clay bed. The deposits, which are covered by a few feet of head, consist of brown, blue and mottled clays, loam, sand and gravel, but the beds change very rapidly, so that adjoining sections present a different sequence. They have yielded numerous species of mollusca and other invertebrata, together with microscopic forms of life represented by the foraminifera. The marine shells were first described by Mr. Whitley, and subse- quently studied by Messrs. S. V. Wood, Robert Bell, and P. F. Kendall, while Mr. Fortescue Millett has been engaged in the investigation of the foraminifera. Finally the beds have been studied by Mr. Clement Reid, who discovered another outlier of these Pliocene deposits on the ridge north of Cannon's Town, at an elevation of 150 feet, in which the fos- siliferous clays of St. Erth are missing. Mr. Reid considers that the 13
