1869.] RTJSCHHAirPT SALT-MINES OP ST. DOMINGO. 257 



The rocks of which the mountain is composed are referred by the 

 author to the " Eed-Sandstone class." Below, where the chief 

 visible salt-deposits occur, the rocks are chiefly gypsum-schists, 

 sometimes very argillaceous, rarely calcareous. The salt is gene- 

 rally 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 Enri- 

 quillo 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. Mtjrchison 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 ]\Iiocene 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 proba- 

 bility 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. Etheeidge was satisfied that the shells from St. Domingo 



