1853.] Report on the Geological Structure of the Salt Range. 269 



Secondary Oolitic Rocks, 

 a. Yellow, iron-stained, quartzose sandstone, grits and bituminous 



shales. 



Besting on the upper carboniferous rocks and separated from 

 them by a few thin beds of a yellow argillaceous limestone, there 

 occur a series of fissile argillaceous sandstones, and coarse quartzose 

 grits and sandstones, generally of an incoherent character, alternat- 

 ing with beds of black bituminous shales charged with iron pyrites. 

 The prevailing colour of the sandstones is a sickly yellow, derived 

 from impregnation with peroxide of iron. Masses of fossil wood con- 

 verted into jet are abundant, both in the sandstones and grits. These 

 also in some places occur in the shales, which, where exposed to air 

 and moisture, are in a constant state of decomposition from the 

 oxidation of their contained pyrites. So violent is the action and so 

 great the heat produced, that sometimes the shales undergo sponta- 

 neous combustion, and whole beds maybe observed either converted, 

 or in process of being so, into a ferruginous claystone of a dark red 

 colour, which occasionally presents a kind of concretionary structure. 



In the neighbourhood of these decomposing shales and claystones, 

 the sandstones and grits acquire a whitened and baked appearance, 

 and the masses of jet they contain, are frequently converted into coke. 



Where the shales are moist, their surface is generally incrusted 

 with an efflorescence of sulphate of iron and alumina, which strongly 

 impregnate the water of springs which issue from them in some 

 ravines, and which on exposure to the air, deposits on the ground 

 over which it flows a crust of hydrated peroxide of iron. In some of 

 the shale beds in the upper part of the series, a magnesian efflo- 

 rescence has been noticed, but the sandstones and grits seem alto- 

 gether free of magnesian impregnation. 



The lower argillaceous beds occasionally contain very perfect im- 

 pressions of the delicate fronds of ferns, converted into black carbo- 

 naceous matter. These are doubtless of fresh water origin and, from 

 the fineness of the sand and mud of which they are composed, must 

 have been deposited in still water. 



The grits which succeed them and contain masses of jet are also 

 probably of fresh-water origin, but the fact of the latter being found 

 only in masses, which are evidently portions of the trunks and 



2 M 



