CHAP. 3.] KADAPAH FORMATION.——CHEY-AIR BEDS. 198 
These chert-like rocks are of various shades of grey and brown 
colors: they are exceedingly hard, scarcely, in some instances, to be 
scratched by the knife, very compact, and very fine-grained. They 
break with a semi-conchoidal or hackly fracture in splinters with a sharp 
and acute edge. The finer varieties show a surface of fracture like that 
of coarse porcelain; and they are not, except in rare cases and when 
the rock is weathered, acted on by acid. They are all fusible with great 
difficulty before the blow-pipe. The darker varieties weather of a white 
color to an exceedingly slight depth from the surface. The thicker beds 
. or bands break up in joints sometimes just like trap, that is, in pillars 
with an irregular polygonal section. They are all more or less lami- 
nated, or seamed with lamine, which are parallel to the stratification of 
the rest of the true aqueous rocks of this series. There is no instance 
of intrusion of these rocks: they all seem to have been regularly 
spread out over the subjacent strata in thin seams. 
One of these seams is amygdaloidal with kernels of calc-spar, and 
| it was mainly the structure of this particular band 
pU which tended to the conclusion that these deposits 
are not cherts but felstone or hornstone. The variety* in question is a 
fine-grained, compact, porcellanie pale grey rock, peppered over with 
minute black speckles, and amygdaloidal with spherieal or rather small 
bean-like assemblages of darker grey glassy cale-spar. The kernels 
weather out, leaving distinct and well-marked cavities. 
This is the only band of these rocks which is vesicular; and 
whether it be a consolidated felspathie dust, or a contemporaneous flow 
of felspathic lava, it is very much of the same composition, except in the 
small quantity of soda, as the other grey beds. 
The term felstone is usually applied to an intrusive rock, but it is 
used also by the Geological Survey of Great Britain for rocks which are as 
* No. 1 of preceding analyses. 
X 
be 
سم‎ 
ی 
w 
دب 
~ 
