100 Notes on Geological Specimens from [Feb. 



distribution of the singular sandstone-like gneiss described by Heyne ; 

 and which, in hand specimens, it is often impossible to distinguish 

 from the sandstone also found in many localities : and I do not know 

 a more interesting subject of inquiry, than that of ascertaining whe- 

 ther this singular rock is metamorphic, and the sandstone altered by 

 the intrusion of the great masses of porphyry so commonly found 

 near these equivocal rocks, and by the numerous greenstone dykes and 

 masses scattered over the whole of these districts. The diamond mines 

 of Mulavelly are at no great distance from Condapilly, to the right of 

 the road, situated in a basin between hills covered with jungle. The 

 sides of which, one-third from the top, were found by Dr. W. David- 

 son to be strewed with a sandstone conglomerate ; but he was pre- 

 vented getting to the top by the approach of night. Fragments of 

 this are found in the gravel, of which I believe specimens have already 

 been sent to the Society, intermixed with much kankar : and from 

 some pits in the valley, most of the lime used in the district is pro- 

 cured. The soil of the country on the Hyderabad Military road, after 

 leaving the alluvial plain above Beirwarah, is formed of decomposed 

 granite, but contains much lime. This admixture, and the kankar 

 nodules, are probably of recent origin ; as I observed, in a valley to the 

 right of the road north of the hill fort of Yeralagundah, about 1 8 miles 

 from Beirwarah, a stream trickling over granite rocks, and depositing 

 lime on all the branches and rocks around. Some pieces of stone of 

 considerable size have thus been formed, and recent specimens, con- 

 taining remains of branches, or of grass, easily crumble to pieces, and 

 are carried away by the stream. The source of the spring I was pre- 

 vented from ascertaining, by the approach of night ; and as an excuse 

 for leaving this and other interesting circumstances unexplored, I 

 must state, that being in Medical charge of the European regiment, 

 during a sickly season, I could not command my own time of marching, 

 or sufficient leisure. 



The character of the granite of the Deccan continues well marked 

 throughout the remaining part of the route to Hyderabad, and dykes 

 and imbedded masses of a fine crystalline greenstone or hornblende 

 rock of great hardness are frequently seen. These last have occasion- 

 ally irregular shapes, and in one or two instances, that of the italic 

 or other irregular curve ; and near Secunderabad, they appear to be 

 connected with the dykes, in the neighbourhood of which they are 

 found. It was also frequently observed, that the various substances 

 entering into the composition of the granite in the neighbourhood of 

 these dykes or masses, formed very large and distinct crystals ; and 

 the imbedded greenstone, though often intimately united with the 



