896 



PRINCIPLES OF STRATIGRAPHY 



and so they are the regions where ancient types persisted, while the 

 region near the oscillation circle (northern North America, north- 

 ern Eurasia, western Europe, Africa, and Antarctica), on the con- 

 trary, showed the greatest oscillation in climate and in life during 

 the successive periods of the earth's history. 



When we next consider what efifects the shifting of the poles 

 would have on the form of the lithosphere we realize that, while 

 it would be more gradual than the effect on the hydrosphere, it 



Fig. 245. Map of the Pleistocenic Tee Period, showing the distribution of the 

 ice and the hypothetical North Pole. (After Walther.) The 

 black dots in western Europe indicate the locahties where re- 

 mains of early man have been found. 



must still result in a series of important changes, if the hypothesis 

 of pendulation is correct. The influence of tlie centrifugal force 

 on the equatorial region is manifested by an expansion or stretch- 

 ing of the equatorial zone, and this will result in the formation of 

 depressions, through the sinking of fault blocks. Depressions in 

 the present surface of the lithosphere are most marked in the 

 quadrant now approaching the equator, near which lie all the large 

 terrestrial or submarine trenches and deeps. Thus the great sub- 

 marine depressions of the present day, the Tonga and Kermadec 

 deeps, lie in the South Pacific quadrant, whereas similar depressions 



