GEOLOGY AND GEOLOGIC HISTORY. 75 



is blue clay-shale or siltstone resembling that so common in the lower for- 

 mations of the Yaque group, especially in the Cercado formation, but is 

 finer-grained and contains only a few fossils. The thickness of the Mao 

 clay is unknown but is probably not less than 150 meters and may be con- 

 siderably more. 



The type exposure is at station 8530 on Plate IX. The few fossils that 

 have been collected from the Mao clay are listed on page 153. 



Cerros de Sal Formation. 

 Around the border of Enriquillo Basin there are strata containing 

 Miocene fossils that are obviously younger than the beds of the Yaque 

 group. For these strata the name Cerros de Sal formation is proposed by 

 Condit and Ross. (See p. 201.) The name is taken from the Cerros de 

 Sal, where salt is mined. 



The stratigraphic relations of the Cerros de Sal formation to the forma- 

 tions of the Yaque group have not been determined, but the presence in the 

 formation of beds of salt and gypsum, evidently formed in enclosed basins, 

 suggests that the Cerros de Sal formation is not conformable with the 

 Yaque group. 



The lithology of the Cerros de Sal formation is shown in the following 

 generalized section, which was measured by Condit and Ross in the Cerros 

 de Sal. The thicknesses given are regarded as minima. 

 Generalized section in the Cerros de Sal. 

 Miocene (Cerros de Sal formation) : Meters. 



7. Sandy shale, poorly exposed, alternating with calcareous 

 fossiliferous sandstone that forms low ridges north of 



Cerros de Sal 300 



6. Cross-bedded sandstone, unconsolidated, alternating with 



gypseous shale; strike N. 70° E 150 



5. Sandy clay beds, light olive color, with embedded corals at 

 two horizons (station 8574); strike about N. 70° W., dip 



vertical 400 



4. Sandy clay beds of various colors with several shell beds 



(station 8742) and thin layers of impure earthy lignite 170 



3. Sandstone, sandy shale, and thin layers of pinkish fossiliferous 



limestone, forming north face of high ridge 150 



2. Gypsum in thick, massive, white, finely crystalline layers, 

 alternating with thinner layers of green, gypseous shales, 

 and with beds of coarsely crystalline salt; gypseous shales 



in upper part 700 



1. Sandy clay and sandstone, red and yellow 100 



The fossils collected from the Cerros de Sal formation are listed on pages 

 163-164. The fauna has no known counterpart on the north side of the 

 island. The Cerros de Sal formation is younger than any other Miocene 

 deposits hitherto discovered in the West Indies. It is provisionally corre- 

 lated with the upper Miocene of Europe — that is, with the Tortonian, 

 Sarmatian, or Pontian stages of the Mediterranean region. 



