Page:Early Man in Britain and His Place in the Tertiary Period.djvu/143

] series of climatal and geograpliical changes, affecting the area of Britain north of the above line, those which are purely local being omitted.

At the beginning of the Pleistocene age the temperature was lowered in northern Asia and Europe, and ultimately became sufficiently severe to allow of glaciers descending from the hills in Britain and Ireland, and covering large tracts of the lower grounds, like the con- fluent glaciers concealing a large portion of Greenland. One of these systems of glaciers covered the greater part of Scotland, another the mountains of Cumberland and Westmoreland, a third the Pennine chain, and a fourth the greater part of Wales, and they have left their marks behind in all these districts in the ice-moulded contours of the hills, and in the grooves cut in the