series of climatal and geograpliical changes, affecting the area of Britain north of the above line, those which are purely local being omitted.
1. The First Glaciation a Period of Elevation.
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
because they tell us nothing as to the contemporary fauna and flora, by which alone all geological periods have hitherto been determined. I am unable, therefore, to agree with Dr. James Geikie in treating the Pleistocene period as the equivalent of "the Ice age." It is foreign to the plan of this work to discuss the much debated cause of the Glacial period, as the lowering of the temperature in the Pleistocene age is frequently termed. Was it due to a change in the oceanic currents? or to a movement in the axis of the earth? or to a variation in the heating power of the variable star on which our universe depends? The question opens a vast field for speculation, on which the reader may consult Dr. Croll's Climate and Time, Sir John Lubbock's Prehistoric Times, and Sir Charles Lyell's Antiquity of Man. The best account of the complex phenomena of the Glacial period is to be found in Lyell's Antiquity of Man, 4th edit. c. xil-xviii. See also The Great Ice Age of Dr. James Geikie, as well as the essays of Jamieson, Searles Wood, Harmer, Hull, De Rance, and others, in the Geological Magazine, the Quarterly Journal of the Geological Society, and the Memoirs of the Geological Survey.
