THE GEOLOGIC HISTORY OF CHINA 



109 



shale, and sandstone, which eventually reached a thickness of 5,000- 

 10,000 feet. 



This condition did not hold without end, for eventually 2 strong 

 compressive forces, engendered in the underlying body of the earth, 

 squeezed the superficial rocks into folds, and thus bulged the surface 

 high above sea level in the region so affected. By the prompt attack of 

 streams, winds, glaciers, and the other agencies which are incessantly 

 sculpturing the surface of the earth, these elevated districts were, even 

 while rising, carved into rugged mountains and deep valleys, so that 

 the original folds were greatly disfigured even before the compressive 

 forces ceased to operate. 



It is a fact generally recognized among geologists, that in terms of 

 geologic time such episodes of compression and folding are short-lived. 

 They are soon followed by much longer periods during which the in- 

 ternal forces of the earth are quiescent, but in which the erosive agen- 

 cies have free play. If any land remains indefinitely above sea level, 

 and is not disturbed by movements from below, the mountains and hills 

 will eventually be worn away and there will be left only a broad almost 

 featureless plain. It is believed that China, in consequence of such a 

 period of quiescence, 3 was reduced to a lowland from which almost all 

 of the preexisting mountains had been removed. In this condition it 

 probably remained for more than one geologic period, and the western 

 part may even have been submerged beneath the sea which at that time 



Fig. 8. Heavily Loaded Freight Fig. 10. Freight Wheel-barrows 



Wheel-barrows with Mules for Mo- rigged to take Advantage of a Favob- 

 tive Power. able Wind. 



Fig. 9. A Typical Passenger Cart. Fig. 11. A Medium-sized House- 



boat USED ON THE YANG-TZE-KIANG AND 



its Tributaries. 



3 Cretaceous and Eocene periods. 



