PORTO RICO 



109 



V(M. CAMC TUFF FORMAT] 



IF THE MOUNTAINS 



The upper part of the Pepino hills is made up at their surface 

 of a rather hard lime marl full of coral heads, with occasional 

 indurated strata of firm white porous limestones. These rocks 

 (the Pepino formation) are of Miocene age, as determined by 

 Mr T. Way land Vau'ghan from the corals collected by me, similar 

 to certain rocks of Antigua hitherto not known in the geologic 

 sequence of the Great Antilles. Their tilted position, standing 

 at 1,200 feet where they meet the older volcanic mass, testifies 

 to the great geologic movements which have taken place in the 

 West Indies in late geologic time. 



Below this limestone, which is at least 100 feet thick, are fossil- 

 iferous greensaud marls of undetermined age (Eocene or Oligo- 

 cene), which in turn rest upon a great thickness of thinly 

 stratified reddish lignitic clays and sands of Eocene age (the 

 Richmond formation) which outcrops near San Sebastian, Guate- 

 mala, and Mocha on the western end of the island, and near 

 Carolina on the northeast coast. 



The south coast hills are composed entirely of chalk}' or other 

 loose-textured glaring white limestone of a very porous character, 

 often chalky, which was deposited around the margin of the 

 mountainous island mass when it was submerged about 600 feet 

 lower than it stands at present. These are largely of Pleistocene 

 age, although some of the lower strata may be as old as the Oligo- 

 cene. Their surface is often covered by the peculiar efflorescent 

 calcareous precipitate known in Mexico as tepetate, which forms 

 .1 shallow subsoil or pan. 



