Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/96

 15 feet; it is entirely excavated in granular massive gypsum or alabaster, veined with blue and grey stripes and occasional patches of clay, the whole being apparently a solid mass. The watercourse was nearly dry on the 9th of April, only a few of the pools below the places where there are small waterfalls in flood-time being filled with small quantities of intensely salt and bitter water, so that it could be easily followed on foot. We traced it up for about 1-1/2 miles, making a very tortuous course, when the cliffs appeared to be getting somewhat lower ; but there was no sign of the gully coming to an end as far as could be seen from the highest point reached. The bottom of the valley is eroded into a smooth and nearly semi- circular channel by the rush of the winter torrents, either in the solid rock or in large tumbled blocks ; while, just above the flood- level, the side cliffs are scored into parallel grooves resembling the fluting of an Ionic pilaster, by the action of water charged with sand trickling down from above. These grooves are about half an inch deep, separated from each other by small sharp-edged ridges. They are, as a rule, vertical, and in the direction of the flow of the water ; and they always end, in the most striking manner, just at the high- water-line.

At intervals all along the valley an old alluvium of gravel and sand with fragments of gypsum, the last being exceedingly rough and irregular in outline, is seen at heights of between 50 and 70 feet. This gravel has been eroded into steep cliffs. The alabaster occurring in this valley somewhat resembles that of Chellaston and Fauld, in Staffordshire, but without the red veins, being only mottled with blue or grey bands of clay instead. The best blocks seen, lying loose on the watercourse and tumbled from the cliffs, cubed about 4 feet on the side ; but it would be difficult to find one of this size perfectly sound, though there are many places where large masses might be got by quarrying. The semitranslucent variety of alabaster, such as that of Volterra, does not occur here ; but nodules of a somewhat similar character were observed in the dark shales further to the north.

Gypsum of Gharandel. — In the lower part of Wady Gharandel the same gypsum-marls appear, in hills of considerable height, say from 300 to 400 feet. The principal feature is formed by a massive bed of opake-white gypsum, overlying dark bluish-green and gray marls and clays filled with selenite in fibrous masses, and occasionally in detached crystals. The large bed breaks up and falls, from the slipping away of the marl below it ; but the tumbled blocks are mostly reconsolidated by the action of water, forming reconstructed beds on the slopes of the shales, which are again subjected to denudation, giving rise to hills of extremely irregular outline and structure. The whole of the surface of the slopes, especially the more prominent, is very rough and uneven, owing to the solvent action of atmospheric water on the gypsum. The more impure and sandy portions, which resist the weather better, form regular saw-backed crestings, so that the process of climbing the hills, in spite of their being mainly made up of clay, is disagreeably like going along a garden-wall