M. Voysey on the Diamond Mines of Southern India. 99 



passes on the Cuddapah road, are those of Bakrapet and Moor- 

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

 and Warripalli on the Ongole road, are among the eastern. 

 The breadth of the range varies, but never exceeds fifty 

 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 or 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 11 I do not mean the Wernerian Thousheiffer, 

 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, 11 then, of the Nalla Malla moun- 

 tains, consists of clay-slate ; of every variety of slaty lime- 

 stone, between pure limestone and pure slate ; of quartz rock ; 

 of sandstone ; of sandstone breccia ; of flinty-slate ; of horn- 

 stone-slate, and of a limestone which I call tuffaceous, for want 

 of a better name, containing imbedded in it rounded and an- 

 gular masses of all these rocks. All these vary so much in 

 their composition, and pass into each other by such insensi- 

 ble gradations, as well as abrupt transitions, as to defy arrange- 

 ment, and render a particular description useless. 



It is bounded on all sides by granite, which everywhere ap- 

 pears to pass under it, and to form its basis. 



Some parts detached from the main range, such as Naggery 

 Nose, Worramallipet, and Nandigaon, a town in the Hyderabad 

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

 summits of sandstone and quartz rock, the basis or remaining 

 two-thirds being of granite. This range of mountains is inter- 

 sected by the rivers Kistna and Pennar, and both appear to 

 pass through gaps or fissures in it, which have been produced 

 by some great convulsion, which, at the same time that it 



