114 ROCK-METAMORPHISM. 



of about 1000/2300, and 5000 feet: it would also appear that 

 these correspond with the main plateaus of Cape-colony. In 

 short, it may be safely stated that marine terraces are to be seen 

 in every region of the globe. 



In the deep valleys of the lofty southern buttress (Gangri 

 range) of Thibet, terraces ascend to the height of 16,000 feet ; 

 but as these may have been formed along the shores of elevated 

 lakes, such as are now in Ladak and adjacent countries, it would 

 be unsafe to classify them with the marine representatives that 

 have been noticed. 



It may nevertheless be maintained that a number of geological 

 evidences afforded by the area last noticed, combined with the 

 proofs already brought forward, establish the conclusion that 

 vertical movements of vast regional extent have affected not only 

 High Asia but the entirety of the earth's surface elevating con- 

 tinents, including mountains and plateaus, at the same time 

 uplifting the bed of the intervening oceans thousands of feet 

 above their present level relatively to that of the sea, or 

 plunging them as deeply in the opposite direction. 



Without denying that the level of the sea may have undergone 

 great fluctuations at intervals during past geological time, caused 

 by seonic flows and ebbs of the ocean, and that such changes may 

 have participated, to an extent far beyond what physicists and 

 hydrographers are at present disposed to admit, in developing 

 phenomena which, for convenience' sake, I have collectively 

 ascribed to vertical movements of the earth's crust or without 

 offering any opinion respecting the hypotheses suggested by 

 Babbage, Herschel, and others as to the cause of phenomena of 

 elevation and subsidence it does not appear improbable that 

 cyclical or periodically recurrent vertical movements, each one 

 representing a vast chronological term, have by slow degrees 

 alternately elevated and depressed opposite areas, corresponding 

 in extent with a continental or even a hemispherical division 

 of the globe. 



To illustrate this view, let it be assumed that one of our con- 

 tinents, having attained its maximum elevation, is next to 

 undergo subsidence* During this elevated period the land" 

 surfaces of moderate height would be in what may be termed the 

 first stage of depositional action, viz. the formation of subaerial, 

 freshwater, and estuarine deposits ; in the second stage the same 



