GEOLOGICAL NOTES ON ASSAM. b'6 



a general opinion that this older alluvium is of marine formation. The 

 more rational views of fluviatile rock formation, so uncompromisingly 

 advocated by Colonel Greenwood,''^ and so graphically illustrated by 

 Mr. Ferguson in the paper already quoted, are to a great extent adopted 

 within the range of the actual river-courses ; but these associated deposits 

 are still looked upon as of a different order. The fact against their 

 belonging to the actual form of conditions is, their higher raised position, 

 apparently quite out of reach of the formative action of rain and rivers. 

 They most commonly appear as a zone between the flat area of actual 

 inundation and the hill-boundary of the plains, but they also show as 

 islands of various extent in the plains. The most direct argument 

 against the purely fluviatile formation of this older alluvium is its dis- 

 similarity to the silt deposits of the delta or the river courses ; its 

 general character is a massive ochreous clay more or less sandy. Mr. 

 Ferguson does not directly discuss this matter of the older alluvium ; 

 but in the only instance of it that comes under his notice, in the high 

 ground north of Dacca (p. 329), he adopts unhesitatingly .the same 

 supposition ; he identifies the rock with that found at Calcutta below the 

 sea level, and he accounts for the elevation by special upheaval. 



I do not at all gainsay the strength of these arguments ; my op- 

 position to them is rather an appeal than an argument, a protest against 

 the use of extreme measures until the simpler ones have been fully tried. 

 I think that the power of atmospheric causes to produce superficial 

 deposits is altogether unappreciated. If the sea, or any water basin, is 

 required for the production of a rock like this older alluvium, it seems to 

 me that a very small part of India can escape submergence within recent 

 times j I do not think this clay can be essentially distinguished from 

 deposits occurring on all the table-lands of Hindustan. If this clay only 

 occurred in what is its most characteristic position, along the border of 



* "Rain and Rivers," 1857. 



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