192 Geohyii of Kortliedsfern Wed India Islands. 



that tliey were largely submerged in the Miocene time, and that 

 after this period a continental uplift occurred in the West 

 Indies. 



Pliocene axd Post-plioce]s^e Formations. — The line of 

 sei^aration between the Miocene and Pliocene formations in the 

 West Indies is nowhere decided. It is possible that the hard, 

 yellowish-white limestone, Avhich contains only few fossils and 

 covers the true Miocene beds, may be more accurately called 

 Pliocene, and not Miocene, as I have done in the foregoing. 

 On the other hand, it is by no means easy to draw a line of de- 

 marcation between the Pliocene and Post-pliocene time. I am 

 inclined to think that the island of Sombrero is of Plioceno 

 origin, also Barbuda and some part of Barbadoes. 



To the Post-pliocene time are to be referred the very import- 

 ant volcanic formations which extend from Saba through St. 

 Eustatius, St. Kitts, Nevis, Redonda, Montserrat, Guadeloupe, 

 etc. In St. Kitts I found, near Brimstone Hill, a white lime- 

 stone formation, containing a large number of fossils, generally 

 impressions and casts. All the specimens, belonging to about 

 forty-three different species, could be identified with living Ca- 

 ribbean species, except only a single specimen of Modiolaria. 

 It is not improbable that tlie elevation of the Miocene strata was 

 accompanied by a subsidence in the Caribbean sea, and that on 

 the limit between the area of elevation and that of subsidence, 

 large fissures originated, pouring out the tufas and other ig- 

 neous products, of which the volcanic islands are formed. 



To the Post-pliocene time may also be referred a limestone 

 formation of great extent, forming the island of Anegada, and 

 the Bahamas. Anegada is a flat, ver}'' low island of limestone, 

 containing great numbers of fossil shells belonging to species 

 still living in the Caribbean sea. Anegada is nearly allied, in 

 its geological structure, to the Bahamas, and proves that in this 

 part of the Caribbean area an elevation and not a subsidence is 

 ffoinc" on. 



