1838.] 



Malcolmson on the Basaltic District of India, 



205 



produced either by infi]trati(3n or sublimation, laU, by molecular atlrac- 

 tion, because calcareous spar is much more rare (han siliceous minei als, 

 though carbonate of lime abounds throughout the basalt. 



Argillaceous Limesio7ie.—Orgnn\c remains have not been noticed in 

 this rock. It consists, in the lower part, of thin strata of compact blue 

 or white limestone, and generally, in the upper, of blue, red, green and 

 white schists, or slaty clay. Siliceous matter occurs in both the lime- 

 stone and schist. Where the formation is in contact wilh the trap, liie 

 limestone is sometimes crystalline, and loses its stratified structure; 

 and at the Pindee Ghat, in the Sichel Hills, the argillaceous and sili- 

 ceous ing'-edients appear to have separated, and the latter to Imve col- 

 lected in bands, having partly the aspect of chalcedony, and in black 

 chert. In some districts the limestone is cavernous, and it is often 

 penetrated by circular cavities, which, the author conceives, were formed 

 by the extrication of gaseous fluids, in the same manner as similar cavi- 

 ties are now produced in the mud by tlie escape of carbonic acid gas. 



A jointed structure, dividing the beds into rhombs, prevails in the 

 limestone, the schist, and the overlying sandstone. The strata are 

 often inclined, apparently the result of dislocation. 



At Jumulmudagur (lat. 14^ 50', long. JS^ 30') the limestone contains 

 layers of muriate of soda; and Mr. Malcolmson is of opinion, that the 

 salt which is found in the alluvial matter, is obtained solely from this 

 formation, as he did not discover a trace of it in the sandstone. 



The limestone and shale are well displayed in the Pennar district, 

 also between the northern foot of the Sichels and Nagpoor; and the 

 author has no doubt that they belong to the same system of strata as 

 the limestone of Bundelcund, described by Major Franklin*, though 

 the red sandstone of that country is stated to underlie the limestone^ 

 while in the region examined by Mr. Malcolmson it overlies. 



Eed Sandstorie.— This fonri'dt'ion is distinguished by containing the 

 breccia in wliich are situated the diamond mines of Golconda, on the 

 banks of the Kistnah, and those on the banks of the Pennar. Where 

 the sandstone rests upon the limestone schist, a gradual passage occurs. 

 The rock is more or less compact, and its prevailing colours are red 

 and white. The diamond breccia is considered by the author, as only 

 a variety of the sandstone in which fragments of older rocks have been 



* Geol. Trans., 2(1 Series, vot. iii., part i., p. 191 et soq., also Asiatic Roscarchos, vol. 

 xviii. p. 21, et seq. An abstract of Major Franldiu's jiaper appeared in riiil, Mag. and 

 Annals, N.S., vol. iv. p. 294. 



