OF SANTO DOMINGO. 87 



geological age of the group of rocks in question. But a careful study of the scanty 

 material at my disposal reveals the existence of a serrated oyster, a Trigonia, a 

 Turritella, shells resembling Ancillaria, JSFatica, Pugnellus (?) and Mactra, besides 

 a Fusoid, one fragment that seems to belong to the group of Pterocera, at least it is 

 an alate shell, bivalves that may prove to be Ouculloea and Lima, and better than all 

 else a beautiful little Ammonite in perfect preservation, and a fragment that I think 

 more careful study will decide to be a piece of a Baculite ! From the above list it 

 will be seen that there can no possible doubt of the Secondary age of the rocks. The 

 Ammonite restricts it so far. The style of the Ammonite besides confines it to the 

 two groups of J urassic and Cretaceous, ^ determination corrobated by the Trigonia, 

 which further belongs to a type much more common in the latter than in the former 

 formation, resembling T. Emoryi, Con., T. Evansana, Meek, and T. Mooraena, Nob. 

 (T. crenulata Roem., not Lam.) In fact I am not sure but that the second of these 

 species is also found in ISTew Grenada, whence it was previously described by Mr. Lea 

 as T. Tocaimaana,'^ and that the present one may have to be included under the same 

 name. The gasteropodous shells are of but little real assistance, although the Ancillaria 

 belongs to a type as yet only known by one or two species high up in the Cretaceous ; 

 the oldest members of the family being in that horizon. The Naiicoid of course has 

 but little weight, while my generic determination of the (?) Pugnellus is not sufficiently 

 sure to warrant me in availing myself of this really valuable aid. 



The Mactra is not of any great stratigraphical value, and the other bivalves are 

 of still less importance. The Baculite, if it should prove to be such, is a little frag- 

 ment so imbedded in the matrix that it will have to be developed by grinding or 

 polishing, since any other process would inevitably destroy it. It will be thus seen 

 that the formation is either Cretaceous or Jurassic, and the preponderance of evidence 

 is in favor of the Cretaceous. This receives additional weight from the results of 

 the labors of other geologists in the Caribbean region. 



Mr. Robert Etheridge examined a small lot of fossils from the coast of Venezuela for 

 the Geological Survey Commissioner of Trinidad, with a view of throwing light on 

 the age of a similar deposit in that island, and reportedf Pteroceras, Cerithium, 

 Turritella, Trigonia subcrenalata,X Ostrea Coidoni, Area, Cardium and JEchinus ;" 

 observing that "the Trigonia may with certainty be referred to the same species 

 obtained at Bogota." 



The Geologists, Messrs. Wall and Sawkins say of the fossiliferous limestones 



* Trans. Amer. Pliil. Soc, Philadelphia, 1840, p. 255, pi. 9, fig. 8. 

 I Report on the Geology of Trinidad, 1860, 2>1. 160. 

 X Most probably identical with Lea's locnimaana. 



