CHAPTER XXII 

 QUATERNARY 



The last great period of the earth's history — the Quaternary — 

 may be considered as beginning with the initiation of extensive sheets 

 of ice in the northern hemisphere. It is divided as follows : 



Quaternary 



Recent, Post-Glacial or Human. Since the disappearance 

 of the continental ice sheets. 



Pleistocene (Greek, pleistos, most, and kainos, recent) or 

 Glacial. Extending from the beginning of glaciation 

 until the final disappearance of continental glaciers. 



Changes at the Close of the Tertiary 



Three important changes at the close of the Tertiary should be 

 noted. 



(i) Elevation. The later Pliocene and early Quaternary was 

 a time of elevation, during which the continents stood higher than 

 now, and broad land connections existed, permitting migration be- 

 tween the continents. On the Atlantic coast the Pleistocene eleva- 

 tion has been variously estimated at from a few hundred to a few 

 thousand feet. Evidence is at hand of an elevation of 1500 feet 

 in southern California, of 3000 to 6000 feet in the Sierra Nevadas, 

 1500 feet in Oregon, and of an even greater raising of the land in 

 British Columbia. In the West Indies, Panama, and South America, 

 observations point to a higher level of the land than now during por- 

 tions of the epoch. An upward movement increased the height and 

 extent of Europe, so that at the time of maximum elevation Great 

 Britain was a portion of Europe, and Europe was united to Africa by 

 broad land connections across Gibraltar and through Italy by way 

 of Sicily. After a time elevation ceased, and a subsidence began 

 which first separated Ireland from Wales and later from Scotland, and 

 finally isolated Great Britain. The land connections with Sicily, 



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