586 



CENOZOIC TIME. 



thickness of the deposits was fully 16,000 feet, with very little lime- 

 stone — the length about that of the Mesozoic (p. 481). But, as the 

 action of rivers during the Cenozoic greatly aided the ocean in wear 

 and transportation., it is probable that this estimate is half too large. 



The data for the Quaternary are very uncertain ; its lapse of time 

 is more plainly marked in the extent of the valleys made than in the 

 thickness of the rock deposits. It must have been at least one-third 

 as long as the Tertiary. 



Adopting these conclusions, the ratio for the Paleozoic, Mesozoic, 

 and Cenozoic would be 12 : 3 : 1. 



2. Geography. — The geographical progress of the Tertiary and the 

 Quaternary ages went forward in different directions. 



A. Tertiary Age. — In the Tertiary, there was (1) the finishing of 

 the rocky substratum of the continents ; (2) the expansion of the con- 

 tinents nearly to their full limits, or their essentially permanent recov- 

 ery from the waters of the ocean ; (3) the elevation of many of the 

 great mountains of the globe, or considerable portions of them, through 

 a large part of their height, as the Alps, Pyrenees, Apennines, Hima- 

 layas, Andes, Rocky Mountains, the loftiest chains of the globe, — a 

 result not finally completed until the close of the Tertiary. 



In North America, there occurred a small extension of the conti- 

 nent, on the Atlantic and Gulf borders ; a vast increase west of the 

 Mississippi ; a small rising of the land on the east and south ; an ele- 

 vation of 6,000 to 10,000 feet in the Rocky Mountains (nearly the 

 whole height of the mass), and 3,000 feet or more on the Pacific 

 border. 



The system of progress during the Tertiary was in each respect a 

 continuation of that which began with the Archaean era. In North 

 America, it was enlargement and elevation, especially to the south- 

 east, south, and southwest, from the original dry land of the Archaean 

 (p. 160). 



The mass of the earth above the ocean's level was increased two 

 or three fold, between the beginning and the end of the Tertiary 

 period. 



B. Quaternary Age. — In the Quaternary, the great events were (1) 

 the excavation of valleys over the lifted mountains and plains, and the 

 shaping of the lofty summits ; (2) the distribution of earth and gravel, 

 covering and levelling the rugged surface of the earth, laying the 

 foundation of prairies, and filling the broad valleys with alluvium ; (3) 

 the finishing of the valleys and lake-borders with a series of plains or 

 terraces, and the extension of flats along the sea. 



There were great oscillations of level in the Quaternary, as well as 

 in the Tertiary ; but those affecting the continents were mainly high- 



