OF SAISTTO DOMIN^GO. 



98 



CHAPTER VI. 



MIOCENE. 



All of that part of the Island which lies north of the Cibao Monntains, except a 

 part of the peninsula of Samana, is made up of Tertiary rocks, usually bordered l)y 

 a narrow strip of more modern age. They also form one or two insignificant de- 

 posits on the south side about San Cristobal and the ISTizao, and are said further to 

 cover a part or all of the valley of the lakes running to Port-au-Prince in Ilayti.* 

 The work of the geological survey not having extended to the latter region I shall 

 confine my observations to the others. 



The district covered by this formation in the nortli, including its extension into 

 Hayti, towards Cape Haytien on the west, and into Samana and south of the bay 

 east, is little less than 150 miles long, although, cutting off these prolongations, it 

 foi"ms a compact area of about 100 miles long by 30 miles wide, or say, in round 

 numbers, about 3000 square miles. Tt abuts against and even overlaps the lower 

 foot hills of the central chain, underlies the whole valley of the Yaqui and Yuna, 

 makes up the entire northern or Monte Cristi range, and sends others along both 

 sides of Samana Bay. In the south it forms a little group of hills extending from 

 near the Jaina River across the J^igua, and thins out in a few isolated patches 

 towards the Nizao. Its total thickness in the vicinity of the ISTigua River is about 

 400 feet, and it is made up of a succession of brown earth}^ and sandy beds, occasion- 

 ally calcareous, superposed on a thin stratum of conglomerate. The top of the 

 series is a rather compact calcareous deposit containing corals. The fossils, except 

 the corals, are usually badly preserved and very meagre in species; a small oyster, 

 two species of Pecten, and some echinoderms being the only recognizable forms. 

 Besides these, a few internal casts of gasteropod shells have been discovered. The 

 corals are so imbedded in their matrix that they can only be collected satisfactorily 

 when they are weathered out, and this same process of weathering is only too apt 

 to destroy the delicate structure of their surfaces. They are however nearly all of 



* Quart. Jour. Geol. Soc. Lond. vol. IX. p. 116. 



Dr. Dickson, of the U. S. Steamship Swatara, kindly presented nie with two or three fossils, too imperfect for 

 determinaiion beyond the facts that they are new to me, and that they are evidently Tertiary. He brought them 

 from Azua, but did not know theii; exact locality. 



A. P. S. — VOL. XV. X. 



