372 Mr. Voysey on the Diamond Mines 



gradually diminish in height, until in the former direction they 

 unite with the sandstone and clay slate mountains of the Go- 

 davery near Palunshah. Their union is certainly not very 

 distinct, but is sufficiently so to entitle them to be considered 

 geologically as the same range. In a southern and S.W. di- 

 rection, they probably extend considerably beyond the Pagoda 

 of Tripati. The most southern point that has fallen under 

 my observation is Naggery Nose, a well known sea-mark on 

 the coast of Coromandel. Travellers to Hyderabad make a 

 considerable detour for the purpose of crossing these moun- 

 tains in their most accessible parts. Among the western passes 

 on the Cuddapah road are those of Bakrapet and Moorcondah 

 on the bank of the Kistna, and those of Nakrikul andWarripalli 

 on the Ona;ole road are among the eastern. The breadth of 

 the range varies, but never exceeds 50 miles. 



The geological structure of these mountains it is difficult 

 to understand, and it cannot be easily explained by either the 

 Huttonian or Wernerian theories. The different rocks of 

 which they are composed, being so mixed together without 

 regard to order of position, each in its turn being uppermost, 

 that it is not easy to give a name so definite as to apply in all 

 places. I once thought the term " shistose formation" would 

 be the most simple and untheoretical term ; but as clay slate 

 is probably the most prevalent rock, I have determined on 

 giving that name to the whole, observing however that by 

 " clay slate formation" I do not mean the Wernerian Thou- 

 sheiffer, the fourth in order, of his enumeration of primary 

 rocks, but merely a collection of rocks which I conceive to 

 have been placed in their present situation at the same period 

 of time. 



The "clay slate formation" then of the Nail a Mall a mountains 

 consists of clay slate; of every variety of slaty lime-stone between 

 pure lime-stone and pure slate; of quartz rock; of sandstone; 

 of sand-stone breccia ; of flinty slate ; of hornstone slate, and of a 

 lime- stone which I call tuffaceous for want of a better name, 

 containing imbedded in it, rounded and angular masses of all 

 these rocks. All these vary so much in their composition, and 

 pass into each other by such insensible gradations, as well as 

 abrupt transition, as to defy arrangement and render a parti- 

 cular description useless. 



It is bounded on all sides by granite, which every where 

 appears to pass under it and to form its basis. 



Some parts detached from the main range, such as Naggerry 

 Nose, Worramallipet and Nandigaon, a town on the Hyder- 

 abad frontier, with many others, have only the upper third of 



their 



