288 Geological Society, 



that which constitutes the great basaltic ranges, by the absence of 

 olivine in the former, though it is common in the latter. The great 

 masses of basalt are also distinguished by being amygdaloidal and 

 more crystalline. 



When en masse the trap overlies the granite, as well as the stra- 

 tified deposits. In the form of veins it traverses the granite, lime- 

 stone, and sandstone, and the freshwater strata are often imbedded 

 or entangled in it. 



In sinking a well near Hutnoor, (lat. 19°38'N., long. 78°30'E,) 

 seams of pure white, pulverulent limestone were found beneath 

 layers of basalt, and calcareous depositions appear to accompany the 

 formation almost universally. With recpect to the minerals con- 

 tained in the amygdaloid s, Mr. Malcolmson is of opinion, that they 

 have not been produced either by infiltration or sublimation, but by 

 molecular attraction, because calcareous spar is much more rare than 

 siliceous minerals, though carbonate of lime abounds throughout the 

 basalt. 



Argillaceous Limestone . — Organic 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 limestone and schist. Where the formation is in contact 

 with the trap, the limestone is sometimes crystalline, and loses its 

 stratified structure ; and at the Pindee Ghat, in the Sichel Hills, the 

 argillaceous and siliceous ingredients appear to have separated, and 

 the latter to have collected 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 cavities are now produced in the mud 

 by the 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. M" 50', long. 78^ 30') the limestone con- 

 tains 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 sand- 

 stone. 



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. 



Red Sandstone. — This formation is distinguished by containing 

 the breccia in which are situated the diamond mines of Golconda, 



* Geol. Trans., 2nd Series, vol. iii., part i., p. 191 et seq., also Asiatic 

 Researches, vol. xviii. p. 24, et seq. An abstract of Major Franklin's paper 

 appeared in Phil. Mag. and Annals, N.S., vol. iv. p. 294. 



