14 Observations on the Geology 



makes it much more perishable than when pure ; and accord- 

 ingly when this is the case, we generally find it wearing down 

 and becoming disintegrated. 



The trap is found under the forms of greenstone and basalt. 

 It is either tabular, massive, or in globular concentric lamellar 

 concretions, with occasionally disseminated crystals of augite. 

 The globular variety is very easily acted on by the weather, in 

 consequence of which it is in many situations completely dis- 

 integrated and converted into a black soil. In some places, 

 where this variety of trap occurs in great abundance, it is worn 

 down into small detached globular masses, which are every 

 where strewed over the ground. 



Almost all the granite of Hyderabad is quickly disintegrated 

 when exposed to the atmosphere, and assumes a globular or 

 irregular form when decomposing. Every where there are 

 immense accumulations of disintegrated granite, at the bottom 

 of the hills and in the valleys. I have known instances of 

 wells being dug through it to the depth of sixty feet, without 

 penetrating to the original rock. At the surface of the ground 

 it is loose, but at considerable depths it is more or less per- 

 fectly consolidated ; and the deeper we penetrate into it, the 

 more perfect is its cohesion. It is not uncommon to meet with 

 small quartz veins running through this consolidated debris, 

 in various directions ; and in many instances there is an ap- 

 pearance of imperfect stratification. 



All the low valleys are covered by a plastic blackish co- 

 loured soil, generally known by the name of cotton ground. 

 It varies in depth from a few feet to many fathoms ; and when 

 a section of it is examined (which can be done in those places 

 where it is worn down by rivers), it is generally found distinctly 

 arranged in strata, which are sometimes separated by thin 

 layers of sand or gravel. These strata vary in thickness, are 

 sometimes horizontal, in other instances waved, or more or 

 less inclined to the horizon. 



I have not had an opportunity of analysing this clay ; but 

 that its composition is by no means uniform, may be inferred 

 from the circumstance of its outward appearance varying con- 

 siderably in different situations. Sometimes it is of a blackish 

 gray colour, and is somewhat friable; while in other cases it has 

 a yellowish or whitish gray colour, and is much more cohesive. 



At first sight one would imagine, that the Hyderabad coun- 

 try has at one time been subjected to the agency of some great 

 destroying cause which has fractured and torn asunder the 

 hills, and precipitated their fragments into the neighbouring 

 plains. But upon closer examination, I think we are naturally 

 led to conclude, that the gradual operation of causes which 



are 



