10 GENERAL OBSERVATIONS ON THE 



It is to the observations of Drs. Heyne and Voysey, that we owe all 

 the information we yet possess of the vallies of the Pennar, the Krishna, 

 and the Goclaveri rivers. This interesting tract of country is not more re- 

 markable as the ancient source of the most valuable productions of the 

 mineral kingdom, being the repository of theGolconda diamonds; — than 

 for the extraordinary geological features which it presents. The Nella 

 Media range of mountains, in which the diamond - breccia is found, is 

 described by Dr. Voysey, as exhibiting a geological structure, that can- 

 not easily be explained by either the Huttonian or Wernerian theories, 

 the different rocks being so intermixed with regard to order of posi- 

 tion, each in its turn being uppermost, that it is difficult to give a 

 name to the formation that will apply in all places : the clay-slate forma- 

 tion is the name he has adopted, under which are included clay-slate, every 

 variety of slaty lime-stone, sand-stone, breccia, Jiinty-slate, horn-stone- 

 slate and a tufaceous lime-stone, containing, embedded in it fragments, 

 (rounded and angular) of all these rocks — all passing into each other by 

 such insensible gradations, as well as by abrupt transitions, as to defy 

 arrangement, and render description useless. It is bounded by granite, 

 which passes under it, and forms its base, some elevated points, such as 

 Naggery Nose, having only their upper third composed of sand-stone and 

 quartz, while the basis is generally granite or sienite. 



The rocks above enumerated, with beds of compact lime-stone, resem- 

 bling lias, of various colours, and the addition of the iron-clay and basaltic 

 rocks, occupy extensive portions of the valleys of the Krishna and Goda- 

 veri, covered in some places by the black trap soil ; a sienitic granite how- 

 ever, composed of hornblende, and sometimes mica, with quartz, felspar, 2indL 

 garnets, interspersed, forms the basis of the ranges that separate these 

 rivers. From Condapilli northward, the granite is often penetrated, and 

 apparently heaved up by injected veins or masses of trap and dykes of 



greenstone. 



