IN THE GAWILGHUR HILLS. 2193 
They are Quartz and Amethyst-quartz. 
Calcedony, and Calcedonic Agates, inclosing 
crystals of carbonate of lime. 
Cach along. 
Common Opal and Semi-Opal. 
Heliotrope. 
Plasma, or transparent Heliotrope, 
Stilbite. 
Analcime. 
Natrolite, 
I chthy oph thai mite. 
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 wacke. With regard to the situa- 
tion of this rock, I think I have rarely seen it on the sum- 
mits of hills, but much more frequently at their bases, and 
forming flat elevated plains. I shall have occasion to ad- 
vert to this rock again when I proceed to describe the fos- 
sil 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 other 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 diluvial soil, commonly called " Black cotton soir of 
India. I have little to add to the former description of it 
Its internal structure is sometimes beautifully developed 
by decomposition, since, in a mass of about six inches dia- 
meter it is possible to count above twelve concentric layers. 
