Page:Early Man in Britain and His Place in the Tertiary Period.djvu/146

118 reduced to clusters of glacier-covered islands rising from the sea, which, in Lancashire and Yorkshire, was not less than 300 feet above its present level. The drift of the icebergs at this time was mainly in a south-easterly direction, as is indicated by rocks derived from Cumberland, Westmoreland, and perhaps Scotland, and dropped, as they melted, over Lancashire, Cheshire, and Shropshire.

At the close of this period the climate grew warmer, and banks of shingle and sand were accumulated, instead of boulder clays, constituting "the Middle drift sand and gravels." The glaciers disappeared, and the sea beat upon an archipelago of islands, which gradually sank beneath the sea to a depth of from 2300 feet below their present level on the flanks of Snowdon, to 1200 feet at Vale Royal, on the road between Buxton and Macclesfield, and to about 1400 feet in Scotland. And as this took place, the sands and shingle gradually arrived at those altitudes, resting on the lower boulder clay in the lower and on the glaciated surface of the older rocks in the higher, grounds. The climate may be inferred to have been temperate, not merely from the absence of icebergs, but from the presence of mollusca now living in the adjacent seas.