1837.] 



the Assam Tea Plant. 



425 



coveries of the late Mr. Scott, at the Colibaree hills, Assam would pre- 

 sent itself as an instance of a great valley of denudation. This would 

 also be supposed to be the case, if the mountains on the two opposite 

 sides possessed any characters in common. Porphyry, primitive lime- 

 stone, serpentine, granite, and talcose slates, compose the mountains 

 on the northern side of the valley, while tertiary sand-stones, shell 

 lime-stone, and coal, compose the southern group ; in conjunction with 

 metamorphosed gneiss, green-stone, and sienite. 



Here then we have two distinct systems, with the valley of Assam 

 interposed between them. The valley contracts towards its outlet, to 

 a breadth of only twenty miles in Lower Assam ; but in Upper Assam, 

 its breadth is probably fifty miles. In Lower Assam the breadth of 

 the valley is still further contracted by a small system of hills given 

 off from the mountains on the south ; through these hills, the Brama- 

 putra flows with a pretty uniform current, at the rate of about three 

 miles an hour. 



At Gowahatti the Mekeer hills, as they are called, are composed of 

 metamorphosed gneiss, consisting of quartz injected into felspar from 

 below, and containing beds of mica. In other places sienite, also 

 containing veins and masses of quartz occurs ; and at Goalpara, horn- 

 blende containing concretions of felspar, constitute the rocks in the 

 immediate vicinity of the river. 



At Noagong the rocks composing a portion of the Mekeers, called 

 Solano, are of a magnesian nature, including lenticular masses of the 

 size of large boulders, of granular and compact quartz, and pebbles of 

 various kinds imbedded in a fine, curved, slaty matrix, and the whole 

 arranged so as to represent the figure of an irregular volcanic cone ; 

 near which, in the open plain, an insulated accumulation of granitic 

 masses form a mound of twenty or thirty feet high. Whether these 

 granitic masses were propelled from below, or projected from a vol- 

 cano, I had no means of determining during my hasty visit to the spot ; 

 but they possess no common character with the other rocks in the 

 vicinity, that I saw. 



Without entering farther into particulars at present, I think 

 it will be conceded, that Assam is not a valley of denudation, 

 and that the mountains on either side not only belong to per- 

 fectly distinct epochs, but that Lower Assam has itself been 

 subject to very considerable disturbances, the effect of which has been 

 to raise the general level of this part of the surface, by which means 

 the waters in the interior were confined for a short time, until the ac- 

 cumulation of silt obliterated the depression within* 



