358 
On some petrified Shells, Spc, 
[Dec. 
Heliotrope. 
Plasma, or translucent heliotrope. 
Stilbitc. 
Analcime. 
Natrolite. 
Icthyoplitlialmite. 
Felspar. 
Carbonate of lime and green earth. . ... 
I have never been able to discover in it, either augite or hornblende in distinct 
crystals. Wien the surface of the land is strewed with these minerals, it is a 
certain indication, that the rock beneath is wacken. With regard to the situation 
of this rock, I have rarely seen it on the summits of hills, but much more fre- 
quently at their bases and forming the flat elevated plains. I shall hare 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 ; l have little to add to the former description of it. Its external struc- 
ture is sometimes beautifully developed by decomposition ; since in a mass ofabout 
six inches diameter, it is possible to count above twelve concentric layers ; and on 
striking the necleus a slight blow with hammer, one or two layers more arc 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 in various stages of decomposition. It isowing 
to the difficulty with which the roots of trees penetrate this rock, that they are so 
rare on its surface, aud never grow to any size ; yet this circumstance does not 
prevent the stndropogon contortion, and Nonius, from growing in the most luxuri- 
ant manner; which sufficiently proves the fertility of the soil. 
On ascending from the Tapti, I observed in a nullah, agroupeof basaltic columns, 
one of which was two feet in diameter, and six-sided. When near the summit of the 
flat table land of Ulan, I entered on a pass, formed on one side by a perpendicu- 
lar section of the rock, from twenty-five to thirty feet, and on the other, by a ra- 
pid descent of forty or fifty. The lower part of the section, as well as the path- 
way, composed of the wacken, or indurated clay of the kind I have before mention - 
ed, of about ten feet in thickness ; lying on it is a stratum of earthy clay, of dif- 
ferent degrees of induration and purity, twenty yards in length, and of about tvvo 
feet in thickness, containing great numbers of entire and broken shells. This 
possesses all the characters of a stratum, since the horizontal fissures are parallel, 
and are prolonged, with a few interruptions, through the whole extent. The accom- 
panying sketch will serve to give a tolerably correct idea of the mode in which the 
stratum appears to overlie the lower rock, and to have been depressed by that 
which is superincumbent* The upper rock consists of about fifteen feet in thick- 
ness of the nodular basalt, or wacken. The nuclei being of all sizes, the vertical 
fissures, which are so remarkable in trap-rocks, are prolonged from both the up- 
per and lower rocks into the shelly stratum, although there is no intermixture of 
substance. 
The stratum is composed of a highly indurated clay, fusible before the blowpipe, 
into a fine black glass, and neither it nor the shells it contains, effervesce in acids. 
The shells are for the most part flattened, and belong either to the genus Conus or 
Volutu. It is not possible to conceive that so fragile u substance as a thin land 
shell shonkl have been so completely flattened without pressure, unless it had been 
previously softened by some mode, which at the same time produced a sufficient 
degree of pressure to effect its flattening. I have attempted, in the annexed sketch, 
to give a representation of the degree of flattening, but I fear that it can only be 
well understood by the specimens themselves. Neither the rock nor its contained 
shells, effervesce in acids. Westward, the ground is covered by the debris of a 
shefly conglomerate, much more indurated and impregnated with green earth, ex- 
hibiting cavities and shells in relief ; from the shape of the former, there can be no 
doubt ot their having once contained shells. Some of the shells are entire, but are 
rarely flattened, The matrix appears to be siliceous, and, in some cases, approach- 
es to imperfect heliotrope. It is not fusible before the blowpipe. 
I may here mention, that in a report to the Marquis of Hastings, in June 1819, 
I mentioned the existence of shells in trap-rocks at Meclconda, at a height of two 
thousand feet above the sea. The liill was composed of nodular trap, and lying on 
