OF SAXTO DOMITs^GO. 



lOT 



says: "]S^or in the West Indies, nor in any other i-egion yet explored, has a bed or 

 formation of coral even five hundred feet thick been discovered so far as we know." 

 Although the coast limestone of Santo Domingo does not reach even half the specified 

 thickness, it is not less a refutation of the objection and a proof of Darwin's theory 

 of barrier reefs. 



The change from gravel through sand and clay beds to this chalky rock in the 

 Jaina country is rejjeated in all of its details in the vicinity of Azua. The gravels 

 of the Southern Yaqui form high hills at las Lagunas on the Constanza trail above 

 the mouth of the Rio de las Cuevas, spread over the plain and extend eastward to the 

 Ocoa River. But as soon as a sufficient distance from the old shore was attained, to 

 allow the current to carry off the mud and fresh water to the eastward, the barrier 

 reef rose to the surface, and its remains exist as a horizontal structure of white 

 earthy limestone, almost entirely non-fossiliferous, and hardening, on exposure to the 

 air, to a rock which breaks with a conchoidal fracture. In this condition it forms the 

 great southern peninsula and the little neighboring Island of Beata. 



The little Peninsula of Samanu is a complete epitome of the geology of the who's 

 island. Except the syenitic intrusions it exhibits every phenomenon discovei-ed and 

 every formation that exists on the main land. • 



The same change from gravel to limestone described above occurs on the southern 

 coast fi'om the vicinity of Santa Barbara to the eastward. About the poi't of Santa 

 Barbara, and especially for a mile or two west the coast hill and the little islands 

 adjoining, are made up of horizontal beds of a coarse gravel with pebbles and even 

 boulders of the metamorphic rocks of the interior. In fact these beds are a perfect 

 index to the geology of the Peninsula. The gi'avel deposit extends but a mile rr 

 two east and west, and penetrates inland to a very inconsiderable distance. But, as 

 has been before stated at Puerto Frances, we again find the coast limestone. 



The coast formation, although it covers such a wide area equal to if not greater 

 than the underlying Miocene, is nowhei'e very thick. From the fact that it is every- 

 where horizontal, it is somewhat difficult to arrive at an accurate estimate of its 

 thickness. ISTowhere along the coast is its base visible, and a vertical measurement 

 inland must necessarily be unfair since it must be made on the thinning out shoi-e- 

 margins of the deposit. Even where it is most elevated above the sea-level a fair 

 measurement cannot be obtained for this I'eason. At Santo Domingo City the bluff is 

 about 40 feet high, and the wells in the city average 50 feet deep. They consequently 

 reach the level of the sea but do not reach the base of the formation. Further back 

 where the surface rises in a series of terraces, the wells still reach the same level 

 before yielding water, but in no case is the underlying rock reached. My Avell two 



