45S 



Sketches of the Meteorology, $c. 



[Oct. 



be very easily examined. They all occur within a space of a few hun- 

 dred yards. I observed several varieties of the hornblende rock. One 

 consists almost entirely of hornblende ; a second contains disseminated 

 crystals of felspar ; a third contains mica and felspar ; a fourth has 

 more of the characters of actynolite than hornblende ; and a fifth con- 

 tains so much mica, that it appears to be almost entirely composed of 

 it. All these varieties, with the gneiss and granite, pass insensibly 

 into each other. They are distinctly stratified ; have a dip of about 30° j 

 and their direction is nearly E. S. E. They form the sides of the 

 chasm, over which the river is precipitated at the falls of Garsipa ; and 

 the depth of which, as already stated, is nearly one thousand feet. 

 This is the only place in India where I have met with primitive 

 gneiss ; but it is not improbable that it occurs in many other parts 

 of the country. We are told by Dr. Davy, that the greater part of 

 Ceylon is composed of it* ; and it is also found in the Himalayasf. 



Quartz veins are very common in the granite. They are sometimes 

 so small as to be capable of being exhibited in hand specimens. Some- 

 times they are of such a magnitude as to form ranges of hills, which 

 maybe recognized at a great distance by their white colour. These 

 hills appear to have originated from the indestructible nature of the 

 quartz having enabled it to withstand the attacks of the weather ; while 

 the more perishable granite was worn down all around it. There are 

 two conspicuous ridges of quartz which appear to have been formed 

 in this way, in the vicinity of Hyderabad. One is near the British 

 native cavalry lines ; the other is near the town of Shumsabad. Drusy 

 cavities, lined with very beautiful amethysts and rock-crystals, are 

 sometimes found in these hills. The granite, in the vicinity of these 

 veins, often passes gradually into the quartz, by losing its other two 

 ingredients. 



Trap is very common throughout the granite tract of India. It is 

 found both in veins and in extensive overlying masses. 



The veins which traverse the granite, present two distinct kinds 

 of trap. One is precisely similar to the most common kind of the 

 secondary or overlying trap, viz. a greenstone of a perishable 

 nature, and having a concentric lamellar structure. It therefore 

 most probably belongs to that formation. The other is more com- 

 pact, has a rhomboidal structure, occurs generally in smaller 

 veins, and is much more durable. 



Large accumulations of granitic debris are met with all over the 

 granite tracts of India. In many places this debris has so completely 

 consolidated, simply by means of the aggregation exerted between its 



* Vide Transactions of the Geological Society of London, Vol. V. p. 314, 

 t Fide do. do. New Series, vol. 1. p. 133, 



