GAWILGERH RANGE OF HILLS. 191 



Common and semi-opaL 

 Heliotrope. 



Plasma, or translucent heliotrope. 



Stilbite. 



Analcime. 



Natrolite. 



Icthyopthalmite. 



Felspar. 



Carbonate of lime and green earth. 

 I have never been able to discover in it either augite or hornblende in distinct 

 crystals. When the surface of the land is strewed with these minerals, 

 it is a certain indication, that the rock beneath is wacken. With reo-ard 

 to the situation of this rock, I have rarely seen it on the summits of 

 hills, but much more frequently at their bases, and forming the flat, ele- 

 vated plains. I shall have occasion to advert to this rock again, when 

 I proceed to describe the petrified shells. 



The nodular basalt is, perhaps, the most common form of trap in this 

 mountain range, as well as in other parts of India. It more commonly 

 forms the surface than either of the rocks, and is as frequently seen on 

 the summits, as it is at the bases of the mountains. It rarely abounds 

 in minerals of any kind. It is the principal source of the rich, black 

 diluvian soil of India, commonly called black cotton soil. I have 

 little to add to the former description of it. Its external structure is some- 

 times beautifully developed by decomposition, since, in a mass of about 

 six inches diameter, it is possible to count above twelve concentric layers, 

 and on striking the nucleus a slight blow with a hammer, one or two more 

 layers are broken off. It is owing to this facility of decomposition, that 

 the annual rains carry down such vast quantities of alluvial soil from 

 its surface, which is, moreover, always strewed with an abundance of nuclei 



ia 



