382 



SCIENCE FROM AN EASY CHAIR 



stratified rock (Jurassic, Triassic, Carboniferous, Devonian, 

 Silurian, Cambrian !), the Pleistocene exhibits but a small 

 thickness of deposit (amounting to but two' or three 

 hundred feet of sand and gravel) as its contribution to 

 the earth's crust. 



Yet, on account of the nearness to our own times of 

 the events which took place in the Pleistocene period, 



FIG. 71. Painting of a bison in orange-brown, grey, black, and white, the 

 outline partly engraved, from the roof of the cave of Altamira, near 

 Santander, in the north of Spain, upon which many others as well as 

 wild-boar, horses, and deer are depicted. The original is about two and 

 a half feet long. These drawings were executed by the Reindeer Men 

 in the period of the Upper or Post-Glacial Pleistocene. 



geologists and prehistorians have studied its details with 

 minute care, and have accumulated an immense array of 

 facts and specimens by digging and carefully collecting 

 in Western and Central Europe. They have divided up 

 this Pleistocene period and the deposits in river-valley 

 and cave which have occurred within its limits into three 

 great consecutive ages. These are distinguished from one 

 another by the distinctive wild animals which flourished 



