Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/95

 bushes recall strikingly the sage-barrens of the desert in the Columbia Valley on the west side of America.

The hills along the northern portion of the desert present no particular features of interest, but form a long and tolerably uniform line of escarpment, not unlike that of the English Oolites or other flat-bedded limestones, and are probably not more than 300 or 400 feet in height. The only marked point is that known as Gebel Sudder, called in addition, on the Admiralty chart, Barn Hill, which rises above the entrance of Wady Sudder.

The hills in the middle distance are those of the gravel-topped alluvium already mentioned as occurring in the same position behind Moses's Wells.

Along the gravel-plain many detached crystals of gypsum, of small size, are met with. They are tolerably perfect, and of the compound arrow-head type, but usually opake in places. This may be due either to exfoliation, attended probably with a partial dehydration, or to a molecular change alone.

Near Wady Amara the raised beach is accompanied by patches of a kind of oolite, made up apparently of rolled fragments of shells, and consolidated into an extremely hard conglomerate, with a decided dip towards the sea. These beds are peculiarly interesting, as bearing on the distribution of organic remains in limestones, and appear to explain why fossils are found so irregularly in different quarries in the same bed. In this case it is evident that the shells imbedded in these consolidated deposits have a much better chance of being preserved than those that are lying about exposed to the air and the sand in the unconsolidated beach all around them. The consolidation is probably due to the joint action of the air and the sea-water ; and it is owing to the latter agent that the deposit has a seaward dip. In future times, after submergence and upheaval, these coarse shelly oolitic patches will most likely appear as lenticular or false- bedded masses in a more compact limestone. The consolidated beaches, with Tridacna gigantea, recall forcibly to the mind of the observer the Calcaire grossier of France.

Alabaster Series. — Approaching Wady Gharandel from the north, the ground becomes more broken as the hills come nearer the sea, and a line of cliff is formed by blue shaly clays, weathering to a rusty brown, filled with nodules and regularly bedded masses of gypsum, both in the form of selenite and dull granular alabaster. The tumbled surface of the marls has been repeatedly rearranged by the formation of fresh masses of gypsum, deposited from solution in the same manner as already noticed in describing the marls near Moses's Wells, but on a much larger scale.

The gypseous series is underlain by calcareous strata at the mouth of Wady Gharandel, but extends for a considerable distance up the valley.

Wady Taragi. — About two miles to the north and a little to the eastward of this point, there is a remarkable section in a small valley called by the Bedaween Wady Taragi. This is about 200 feet deep, and in places more, with a breadth at the bottom of only