1840.] 



of ilie Great Basaltic Dhtrki of India. 



71 



nor could I detect any titanium in it. With regard to the geological 

 relations of the magnetic iron ore, it is also necessary to observe, that 

 in India it is not confined to the hornblende schist, but is found ex- 

 tensively distributed in the granite and gneiss of the Carnatic and 

 Mysore, in quartz rock near the iron v^^orks of Porto Novo ; and, as has 

 already been observed, associated with galena in the diamond sandstone 

 of Cuddapah. The discovery of a mineral, so generally confined to the 

 primary rocks, in the great sandstone formation, affords an additional 

 argument in favour of the opinion of those, who consider this rock and 

 the subjacent schists, as equivalents to the older European sedimentary 

 formations, rather than to those of the supermedial order. 



Description of the Sichel Hills, and of the Fkkshw.4ter Shells. 



Returning to the line of route, the granite, on approaching to the 

 Sichel hills, becomes softer and decomposes rapidly ; and the soil gradu- 

 ally changes to the well-known black basaltic mould, known in India by 

 the name of " cotton ground," and, as usual, it is mixed with calcedo- 

 nies, zeolites, &c. Amongyt these minerals were some fragments of a 

 red colour, and considerable specific gravit}^, though Ml of irregular 

 cavities, and so like the slag of an iron furnace, that I considered them 

 to have had that origin, till I discovered a considerable mass of a similar 

 nature protruding from the granite and black soil b^' which it was cover- 

 ed. Along with these fragments were others of a seniivitrified matter, 

 containing small white crystals of felspar, and hardly to be distinguished 

 from a piece of granite fused by Dr. Voysey in the steel furnaces of the 

 neighbouring district. The granite constitutes the surface rock a little 

 further, gradually passing into a black compact basalt, intermixed with 

 many white spots, apparently of felspar. The trap then becomes softer, 

 forming small hills of a cellular amygdaloid, abounding in cavities lined with 

 green earth, and many of them filled with calcedonies, zeolites, quartz 

 crystals, and, more rarely, calcareous spar, of the sam.e kind as those, so 

 remarkable for their beauty, in the portion of this formation described by 

 Colonel Sykes (Geological Transactions, vol. 4, p. 422*). The crystals 

 also occur in seams, or are diffused through the trap ; and in both cases 



* A beautiful variety of cliabasie, havinj? the angles replaced by tiiangular or penta- 

 gonal faces supporting a rhomboidal surface, of wliicli beautiful specimens abound in 

 certain localities of the -western portion of the formation, has not bpen met with in 

 this neighbourhood ; but, like some other minerals of the basaltic district, it is not 

 generally diffused in the rocks where it is most abundant ; so that I have travelled for 

 several hundred miles without meeting with it. 



