782 On the Physical Geography of the Himalaya. [Aug. 



And as, even to the westward, the sandstone range, with its contained 

 Dhuns, is by no means constant, it may be desirable to attempt to 

 characterise the lower region considered as a whole without reference 

 to local peculiarities or too rigidly defined subdivisions. Now I con- 

 ceive that the lower region owes its distinctive character as a whole to 

 the vast mass of diluvial detritus which was shot from the mountains 

 upon the plains, like gravel from a cart, at some great geological epoch, 

 and which has been, since its deposit, variously and often abraded both 

 in degree and direction, by oceanic, and, in a far less degree, by ordin- 

 ary, floods. Where there was, at the epoch in question, no sandstone 

 range to intercept the downward spread of the debris, this debris would 

 necessarily be carried further south, and be of less thickness ; where 

 there was such a barrier, it would be carried less far southward and be 

 accumulated in greater thickness, especially within the barrier ; and, 

 in like manner, where no sandstone range existed, but only spurs, sent 

 forth, like bent arms, upon the plains from the mountains, the embayed 

 detritus would still be deeply piled and lofty within such spurs,* and 

 thinly and unequally spread without them, by reason of the action of 

 the spurs on the currents. Again, where, as from Gowhatty to Sad- 

 dia, there was not room upon the plains for the free spread and deposit 

 of the descending Himalayan detritus owing to large rapid rivers and to 

 other chains, both parallel and proximate to the Himalaya, the phceno- 

 mena created elsewhere by the more or less unrestricted spread of the 

 Himalayan detritus over the plains, would necessarily be faintly, if at 

 all, traceable. Lastly, if at the time of the descent of the debris, there 

 existed a great dip in the Gangetic plains from N. "W. to S. E., the 

 lithologic character, as well as the distribution, of the debris, would be 

 materially affected thereby ; for, the subsiding oceanic current would have 

 a set from the former to the latter quarter, and would continue to lash 



* There is a signal example of this on the road to Darjiling via Pankabari where 

 the debris, embayed by a spur, is accumulated to several hundred feet, and where 

 moreover there is outside the spur a conspicuous succession of terraces, all due to 

 oceanic forces, and clearly showing that the subsidence of the sea was by intervals, 

 and not at once. Constant observation has caused the people of the Tarai to dis- 

 tinguish three principal tiers of terraces, from the prevalent growth of trees upon 

 each. The highest, is the Saul level ; the middle, the Khair level and the lowest, 

 the Sissu level ; Shorea, Acacia and Dalberga being abundantly developed on the 

 three levels as above enumerated. 



