Page:Early Man in Britain and His Place in the Tertiary Period.djvu/147

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The next change was one of climate, which reverted to the cold condition of the second of these divisions. Glaciers again covered the higher grounds, and icebergs again floated over the lower grounds, still submerged, depositing as they melted the upper boulder clay, which rises as high as 500 feet above the sea-level in Lancashire and Yorkshire (Hull). The drift of the icebergs was south-easterly, since the peculiar altered chalk of Antrim, in the north of Ireland, is scattered over Lancashire and Cheshire, and as far south as Ironbridge in Shropshire.

Then followed an upward movement of the land, until the upper boulder clay became dry land, and Britain and Ireland became part of the mainland of Europe, as is represented in the Map (Fig. 32). Glaciers still remained on the higher hills in Scotland, Wales, and Cumbria, leaving in their retreat the old moraines, so conspicuous in those regions. The climate was less severe than in the preceding period, and was gradually again becoming temperate. As the upper boulder clay deposited on the sea-bottom became lifted up, it was gradually covered by forests of yew, Scotch fir, oak, ash, and alder, in which the Pleistocene mammalia found ample food in the eastern and midland counties.

Similar climatal changes have left their mark upon the higher mountains of Europe, Asia Minor, and North