GLACIER ACTION. 133 



earth's motions, and partly in consequence of the shift- 

 ing distribution of land and sea, what at one time has 

 been tropical, at another becomes arctic, and what at one 

 time has been arctic, at another becomes tropical. 



Astronomers tell us that more than 200,000 years 

 ago, the earth was so placed in regard to the sun, that a 

 series of physical changes was induced, which eventually 

 resulted in conferring upon our hemisphere a most 

 intensely severe climate.* All the northern lands of 

 Europe were then covered with a thick crust of ice 

 and snow. The climate of England and Scotland was 

 what Greenland is now. 



Glaciers, laden with boulders, some torn from the 

 rocks on which they rested, some fallen from over- 

 hanging heights, flowed down the valleys, leaving their 

 ice-tracks along the sides of the hills. When the 

 glaciers melted, they dropped the boulders which they 

 contained, either on the land, or in the sea, far away 

 from the place from which they had been reft from the 

 rocks. Then was laid down the boulder clay, con- 

 sisting of an agglomeration of ground-down rocks of 

 various kinds, old red sandstone, chalk, or coal, inter- 

 spersed with boulders, pebbles, and sometimes shells. 



There must have been constantly recurring alterna- 

 tions of climate, from arctic frost to tropical heat, though 

 separated, it might be, by hundreds of thousands of years, 

 before the dry land was prepared for the occupation of 

 man. Again, every bed of coal presumes an elevation 

 of the land, and a subsequent depression. Near New- 



* Geikie's Great Ice Age, p. 561. 

 7* 



