1842.] of the Himmalay a Mountains. xli 



tually known, as distinguished from what may be considered matter of 

 opinion or inference, subjoining an attempt to combine these details 

 into something like a systematic view of the general structure of the 

 tract, adding such inferences and illustrations as have occurred to me 

 in reconsidering the subject. In the geological details, I shall follow 

 out the extent of each rock as yet observed separately, and in the order 

 in which they actually occur, beginning with the highest zone, and de- 

 scending gradually to the plains. 



Section II. 

 GEOLOGICAL DETAILS. 



78. In the zone of the Himmalay a, the only rock which I have yet 

 observed, I mean as covering any extent, that is, as constituting a forma- 

 tion, is gneiss ; other rocks are found it is true, but only in the form of 

 veins or beds. Gneiss has been traced from Deao, opposite Muzzoolea 

 near Seran in the western corner of the Survey, by Brooang in the valley 

 of the Buspa, and thence ascending to the Snowy Pass of the same 

 name, leading into the valley of the Pabur. In this line the varying 

 level, (5,500 to 15,000 feet,) leaves no doubt of the great thickness, as 

 well as lateral extent of this formation. It is not, however, every where 

 equally obvious, the coating of debris being often of great thickness and 

 covered with luxuriant vegetation. Frequently the only trace of its oc- 

 currence consists in large angular blocks lying on the surface or im- 

 bedded in the coat of debris. This may perhaps be considered incon- 

 clusive evidence of the existence of this rock as a formation, but the 

 case admits of no other, and the same difficulty meets us at every 

 step in these mountains, and as no fragments or any other traces occur, 

 or any other rock in this tract, with the exceptions I shall presently 

 mention, we shall find a difficulty in saying what rock is found below 

 the surface, if we find it necessary to deny the existence of gneiss. 



79. This rock is of the most ordinary character in the greatest 

 number of instances, consisting of quartz, felspar, and mica, and nearly 

 in the usual proportions. It seldom contains any foreign imbedded 

 mineral. The felspar is almost always white, seldom grey, and only 



