OlSr TIIK TOPOfiP.APllY AND C4EOLOGY 



the massive forms, and ai-e so thoroughly fossilized as to be well ada]ited for 

 polishing. 



But while the formation is so small in area and so unsatisfactory in general char- 

 acters on the Santo Domingo side, it becomes, in the Cibao, the most interesting on 

 the island. Cut through by all the tributaries of the Yaqui the sections are 

 numerous and excellent for study. Its local modifications are well illustrated by 

 sections innumerable, into and across the Monte Cristi range on one side, and into 

 the southern hills on the other. In short, it would be diflftcult to find a region where 

 the facilities furnished to the geologist are greater, or where the results could be 

 more certainly arrived at. Add to this that a larger part of the formation is highl}^ 

 fossiliferous, and that the fossils, whether shells or corals, are almost always i)i'e- 

 served entire and hard; as beautiful as the famous fossils of the Paris basin, or as 

 the less known though equally beautiful specimens from Jackson, Mississip])!. 



The entire thickness of the formation in the Cibao is probably over 1.500 and 

 under 2000 feet. It is made up of coarse sandstones at the base, sometimes bearing 

 \)eds of conglomerate, which are however rather local in extent. These beds are 

 best developed between the Bao and the Yaqui, where, being uptilted, their thick- 

 ness is best seen, and are about 600 feet thick. They gradually merge into graj^ 

 shales, which form a ti'ansition to the heavy blue shale beds underlying the town of 

 Santiago, and called by the English Palaeontologists the ISTivaje shale. The upper 

 part of this member is always of a light yellowish brown or bulf color and some- 

 times, especially at its ni)per part, contains beds of sandstone. The whole of this 

 shale member may be safel}^ estimated at about 800 feet of average thickness. The 

 remainder of the formation, say 400 feet more in all, varies locally. It caps the 

 greater part of the Monte Cristi range, and while, north of Moca it forms high bluffs 

 of a nearly white earthy rock, in which it is doubtful whether the argillaceous or the 

 calcareous ingredients preponderate, it foi'ins north of Esperanza sheets of a compact 

 limestone, which, less pure, forms the cap on the isolated table-mountain of Monte 

 Cristi. i^ear Cevico it appears as an impure lime-rock containing corals and 

 foraminifera, and similar beds occur also on Samana and south of SaA^ana la Mar ; 

 while the caves of San Lorenzo, in the same beds, are in a hard, coarse-grained, 

 calcareous sandstone. Nov do the variations cease here. Neav the mouths of the 

 ancient Miocene rivers running from the then much smaller islands now constituting 

 the Cibao Mountains, and among Avhich the Mao was probably the largest, the 

 gravel debris of these streams was deposited, occasionally alternating with a bed of 

 coarse sandstone, synchronously with the formation of the coral reefs and beds of 



