244 GEOGNOSY OF INDIA. 



primitive rocks rest sandstone, and a limestone resembling 

 in some of its characters the lias of England. The well- 

 known diamond-mines of tliis part of the peninsula are 

 situated in the sandstone districts of these rivers. The 

 Krishna is much richer in gems than the Godavery, or prob- 

 ably than any other river of Hindostan. The waters of 

 the Krishna and Godavery, as they approach the sea, divide 

 into numerous branches, and deposite their mineral contents 

 during inundations over the low level tract that separates 

 them. These deposites consist, according to Heyne, of a 

 black earth, composed of the debris of__trap rocks, and of 

 decayed vegetable matter washed from the extensive forests 

 through which these rivers flow. A characteristic ditier- 

 ence may be pointed out in regard to the alluvium of the 

 principal river of the south,— the Cavery. This river, 

 flowing in a long course through the Mysore country, over 

 an extensive and generally barren surface of granitic rocks, 

 with scarcely any woods or jmigle on its banks, se^ms to 

 bring down little or no vegetable matter, but a rich clay, 

 produced from the felspar which predominates in the gran- 

 ites of the south, intermixed with decomposed calcareous 

 conglomerate, rendering the plains of Tanjore the most 

 fertfle portion of the south of India. Onwards to Viza- 

 gapatan and Ganjam syenite and gneiss predominate, and 

 are occasionally covered with laterite. The granite and 

 syenite at Vizagapatan contain numerous unbedded gar- 

 nets. This variety of granite passes into the province of 

 Cuttack. Granite and syenite, with their usual accompa- 

 nying stratified primitive rocks, form the basis and principal 

 elevations of this district. Sandstone extends over a great 

 part of the district of Cudapah : it is in this sandstone, or 

 amid its debris, that some geologists place the original 

 repository of the diamonds found in this part ot India. 

 Coal is reported to occur here, and the sand and loam of 

 the Mahanuddy, besides diamonds, afford grains of gold. 

 Granite and gneiss, covered more or less completely with 

 sandstone and laterite, continue onward through the dis- 

 trict of Medinpur, and thence northward by Bishenpur and 

 Bancora to Birbhum. At Bancora the calcareous rock 

 named kankiir begins to cover the surface of the gramte 

 and syenite rocks which rise above the surface to consid- 

 erable elevations. 



