Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/353

 The rocks of which the mountain is composed are referred by the author to the " Red-Sandstone class." Below, where the chief visible salt-deposits occur, the rocks are chiefly gypsum-schists, sometimes very argillaceous, rarely calcareous. The salt is generally surrounded by an ash-like mass, consisting of gypsum and clay. The higher part of the mountain is formed of gypseous rock not forming connected layers ; this is compared by the author to the gypsum of the Keuper.

The salt-bearing beds are said by the author to be thrown up into a perpendicular position, and this upheaval is described by him as occurring for miles both in the hills and on the low savanas. Numerous salt- springs occur at considerable distances around the mountain.

About eighty holes have been opened by the natives upon the ridge of the mountain in order to get the salt. On the north side an immense ledge of salt is exposed, the soil having been washed away from it. The part exposed is from 250 to 300 feet broad, and is about 200 feet from the base of the mountain.

By an examination of the whole district the author has satisfied himself that the salt-deposits extend not only through the whole of the Cerro de Sal, but also down into the plains below. The adjacent hills to the north-west also bear positive evidence of containing extensive salt-deposits. The supply of salt in the great lake Enriquillo is maintained by the filtration of water down to the beds of salt and then out into the lake. The salt obtained is generally of superior quality.

Discussion.

Sir R. I. Murchison had been at a loss to understand how such beds of salt could coexist with shells said to be of recent species in St. Domingo. The question seemed, however, to have been solved by the fact that these shells are of Miocene age. The geological survey of many of the West-Indian islands had determined that nearly all these deposits were of Miocene age. In the majority of the islands there were no rocks so old as the Cretaceous ; and he therefore suspected that there must have been an error on the part of the author in regarding the beds of St. Domingo as belonging to the Trias. The salt of St. Domingo is therefore of the same age as that of Wieliczka in Poland.

Prof. Ramsay thought it was more remarkable that any salt- deposits of the New Red Sandstone should exist than that there should be so many of Miocene age. There was not much probability of great salt-deposits of more recent date, as there had hardly been sufficient time for their formation, though in the Great Salt Lake and elsewhere such deposits were now forming. The reason why such old deposits of salt had been preserved appeared to be that the salt had been hermetically sealed up in impermeable marl as soon as the part of the salt which lay near the outcrop of the beds had been dissolved away.

Mr. Etheridge was satisfied that the shells from St. Domingo