' Geology, J 83 



ready mentioned) interrupts its continuity. From thence it breaks into a 

 succession of parallel ranges, inferior in elevation and in unbroken conti- 

 nuity, to the western chain, and in the further progress northward after 

 breaking off into subordinate hilly ranges, occupying a wide tract of unex- 

 plored country, and affording vallies for the passage of the great rivers that 

 drain nearly all the waters of the Peninsula into the bay of Bengal. This 

 eastern range may be said to terminate at the same latitude as that of the 

 commencement of the western. Granite rocks, and principally sienite, 

 seem to form the basis of the whole of these eastern ranges, appearing at 

 most of the accessible summits from Cape Coraorin to Hydrabad. Gneiss 

 and mica-slate, that form the sides and base of the mountains, are some- 

 times seen, as also clay-slate, hornblende, slate, flinty-slate, chlorite, and 

 mica-slate, and primitive or crystalline limestones, affording, in some 

 places, marbles of various colours, as in the district of Tennivelly, where 

 also granite appears rising above the surface, in remarkably globular con- 

 cretions, and in perfectly stratified masses, forming low detached hills near 

 Palemcotta, the strata of which dip at an angle of about 45° to the south- 

 west. Partial deposits too of^ overlying rocks exist in this district, and of the 

 black cotton soil, which is supposed to be produced by the debris of trap. 

 In the neighbourhood of Pondicherry there are beds of compact shelly 

 limestone, and some remarkable siliceous petrefactions, chiefly of the ta- 

 marind tree, which have never yet been well described. The beds of the 

 Cavery, or rather the alluvial deposits in the vicinity of Trichinopoly, 

 produce a variety of gems, corresponding to those of Gey Ion. In general, 

 however, the surface of the level country, as far north as the Pennar river, 

 seems to consist of the debris of granite rocks, and plains of marine sand, 

 probably left by the retreat of the sea ; with occasional fresh water alluvial 

 deposits, and partial beds of iron-clay arid detached masses of the overly- 

 ing class. In approaching the Pennar river, the iron-clay formation ex- 

 pands over a larger surface, and clay, slate, and sandstone begin to appear. 

 On the hills behind Nellore are found specimens of a very rich copper ore, 

 yielding from fifty to sixty per cent, of pure metal, according to Dr Heyne, 

 besides argentiferous galena. 



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 Kistna, and the 

 Godavery rivers. This interesting tract of country is not more remarka- 

 ble, as the ancient source of the most valuable productions of the mineral 

 kingdom, being the repository of the Golconda diamonds, than for the 

 extraordinary geological features which it presents. The Nella Malla 

 range of mountains, in which the diamond breccia is found, is described, 

 by Dr Voysey, as exhibiting a geological structure that cannot easily be 

 explained by either the Huttonian or Wernerian theorists ; the different 

 rocks being so mixed together with regard to order of position, each in its 

 turn being uppermost, that it is difficult to give a name to the formation 

 that will apply in all cases. The clay-slate formation is the name he has 

 adopted, under which are included clay-slate, every variety of slaty lime- 

 stone, sandstone, quartz rock, sandstone breccia, flinty-slate, hornstone 

 slate, and a tufaceous limestone, containing imbedded in it fragments. 



