PANGONG: A GLACIAL LAKE 



617 



desiccation has not been continuous in the fashion illustrated by the 

 Hne A, Fig. 16, nor has it been interrupted merely by periods of 

 rest, as shown in B, but rather it has 

 been oscillatory, like C, now drier, 

 now wetter, but the tendency to aridity 

 generally greater than its opponent. 

 The changes appear to be of precisely 

 the same nature as the much larger 

 changes which characterize the glacial 

 period with its alternating glacial and 

 interglacial epochs. If the oscillations 

 are merely local, their study is of com- 

 paratively small importance; but if, as 

 there is reason to believe, correspond- 

 ing variations are taking place simul- 

 taneously over vast areas, they demand 

 the closest study. There seems to be 

 nothing except size to differentiate 

 them from glacial epochs, and as they 

 are even now in progress, their study 

 can be carried on at close hand, and 

 may perhaps be helpful, not only in 

 .solving the secret of the cause of the 

 glacial period, but of the part played 

 by chmate throughout the whole course 

 of geological history. 



Fig. 16. — Diagram to illustrate 

 the course of dessioation at Pan- 

 gong. The horizontal ordinate 

 represents time, and the vertical 

 the condition of climate, wetter or 

 colder upward, drier or warmer 

 downward. 



