CHAP, v.] FIRST GLACIATION A PERIOD OF ELEVATION. 115 



series of climatal and geographical 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 tempera- 

 ture was lowered in northern Asia and Europe, and ulti- 

 mately 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 Pleisto- 

 cene 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 1 or to a 

 variation in the heating power of the variable star on which our universe 

 depends 1 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. xii-xviii. See 

 also The Great Ice Age of Dr. James Geikie, as well as the essays of 

 Jamieson, Searles Wood, Harmer, Hull, De Ranee, and others, in the 

 Geological Magazine, the Quarterly Journal of the Geological Society, and the 

 Memoirs of the Geological Survey. 



