GLEANINGS 
IN 
SCIENCE. 
JYt o. 26. — February, 1831. 
* 
I - — On the Minerals in the Rdjmahal Hills. 
[Continued from p. 8.] 
% 
§ 2. — Western range. 
In the former division, I have said, that the most predominant rock is of the na- 
ture of whin or trap, and quartz is there rather an uncommon ingredient, at least in 
masses of a great size ; but here a large proportion is quartz, and a still greater, a 
kind of rude jasper or petrosilex, called hornstone by the later Mineralogists ; 
and these two siliceous stones run so into one another, by various gradations, that 
it is difficult, if not impossible, to say where the one begins and the other ends. 
It is, I imagine, difficult to say, that these hills are in any degree stratified, although 
they sometimes assume an appearance of that form. In general, the siliceous rocks 
are intersected by a vast number of fissures, horizontal and vertical, cutting them in- 
to masses approaching to the form of cubes and parallelopepids ; and when they are 
exposed to the weather, in a state of decay, these masses divide in to layers some- 
what like those of wood, especially if the mass is exposed on an abrupt vertical 
Surface ; but if the surface exposed is horizontal and level with the earth, the lay- 
ers more resemble slate. In some places the vertical fissures, extending the whole 
depth of a perpendicular rock, give somewhat the appearance of basaltic columns, 
which may be especially observed in the magnificent recess called Marak, about 15 
or 16 miles southerly from Mungger ; but in fact, so far as I observed, there is no- 
thing really columnar in the district. 
These hills are particularly distinguished from those of Rajmahal, by their rugged 
nature, vast masses of naked rock projecting every where on the surface, and form- 
ing precipices of great height and abruptness. 
The form which the greater part of this siliceous stone assumes, is that which 
I have called rude jasper or petrosilex, the hornstone of modern writers ; for although 
these stones are considered as different, yet in the specific characters which are given, 
there is, as often happens, no real difference. If we take the character of Wallerius, 
that petrosilex is found only in veins 1 , or detached masses immersed in rocks, and 
that jasper forms whole rocks, then undoubtedly our rock is a jasper, but it in ge- 
neral departs very tar from the appearance of what is usually called such. It is a rock 
This practice of naming rocks from their position or mode of occurrence, so 
baneful to any thing like correct observation, is not confined to Wallerius. Many 
modern geologists are equally open to censure in this respect. — E d. 
NEW SERIES NO. II. 
