Page:A Treatise on Geology, volume 1.djvu/221

 CHAP. VI. lower part more distinctly splits into sandstone (above) and conglomerate (below) as we approach Nottinghamshire, Derbyshire, and Yorkshire. Here the series becomes triple.

The abundance of red oxide of iron in almost every part of this and the older Permian system deserves the more attention from the fact, that it is in general an investing substance—a sort of varnish covering the white clear rounded grains of quartz which compose the main part of the sandstones of these systems.

Rock salt occurs in the state of clear white cubically crystallized masses, or reddened by the argillaceous sediments among which it occurs: sometimes in Cheshire the red salt is fibrous. Brine springs, which issue from rock salt, contain combinations of iodine and bromine, though in the rock itself those substances can hardly be detected: a circumstance depending on the extreme solubility of the iodic and bromic salts.

Gypsum, a very frequent product of the red argillaceous members of this system, and very commonly found in the vicinity of rock salt, is granular at Chelwerton near Derby, but generally fibrous, as at Tees Mouth, Pocklington, Nottingham, Aust Passage. Sulphate of strontian forms nodules in these marls in Somersetshire.

Organic Remains.—In England we have scarcely an example of the true flora and fauna of this system; for the ramified leaves (Dictyophyllum) of the sandstone near Liverpool, and the almost traceless calamities in marl