140 MIDDLEMISS: PHYSICAL GEOLOGY OF SUB-HIMALAYA. 



that the crust is in a " condition of approximate hydrostatical equili- 

 brium, such that any considerable addition of load will cause any re- 

 " gion to sink or any considerable amount denuded off an area will 

 u cause it to rise," and, therefore, that there must be a " fluid substra- 

 tum " on which the crust floats. He writes, p. 80, — "The Himalayan 

 "area presents some peculiarly interesting features in this connection. 

 "The Sub-Himalayan range consists of tertiary strata which are now 

 M highly disturbed. All, with the exception of the lower portion, which 

 "is nummulitic and consequently marine, are composed of sub-aerial 

 " deposits, formed by detritus brought down by torrents from the 

 " Himalayas. These deposits are together between 12,000 and 15,000 

 " feet thick. The sandstones, which form the chief portion of these 

 " beds, and the red clays which are intercalated with them, are exactly 

 " like the alluvial deposits of the plains. ' Thus it was suggestive, and 

 " not altogether misleading, to say that the Siwaliks were formed of an 

 " upraised portion of the plains of India/ 1 The surface movements in- 

 dicated by this history suggest a level area at the foot of the Hima- 

 "layan range, sinking continuously during the former part of the 

 11 tertiary period. Then a great movement of lateral compression and 

 " elevation took place. Again it sunk, and unconformable beds were 

 " deposited. These were again elevated and compressed. Such at 

 " least appears to be the interpretation of the description given by 

 " the surveyors. But the point which is material to our present subject 

 " is the sinking of the land surface to the depth of nearly three miles, 

 "while river deposits to that thickness were being laid down; the 

 " whole being denuded off mountains whose spoils have in more recent 

 " times provided materials for the great plains of India, and still 

 " those mountains stand the highest in the world. That a sinking of 

 "the area of the plains of a similar character is yet in progress, is 

 "shown by the boring at Fort William, near Calcutta, in which to 

 " the depth of 400 feet fresh-water deposits occurred. The con- 

 " elusion seems irresistible that corresponding to the long, though 

 "occasionally interrupted, depression of these plains, a correlative 

 1 Manual of the Geology of India. 



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