Bland.] "-^ [March 3, 



embraced in section IV, and should add that Dentellaria does not occur in 

 those Islands. Helix predominates over Bulimus in North America and 

 the Islands in Sections I., II., III., and IV, while the reverse is the case 

 in South America, and there is at least an increased proportionate num- 

 ber of Bulimus, as compared with HeUxiw Section Y. 



I have spoken of a "ridge" on which the Islands in subdivision 2 of 

 that section stand (St. Lucia excepted), and must remark in addition, 

 that there may have existed an extension of the South American Con- 

 tinent, from the eastern boundary of Guiana to some point west of the 

 Grenada bank, and running North to the neighborhood of the Anguilla 

 bank, on the western side of which extension there was the fauna now to 

 be studied in the Islands from St. Lucia to Trinidad, and on the eastern 

 side, in those from the St. Christopher and Antigua banks to Barbados. 



Reference has been made to the similarity of depths in nearly the same 

 Latitude between Jamaica and Cuba, and Saba and the Virgin bank. 



Mr. Rawson has directed ray attention to a comparison of the Ibllowing 



depths in the Caribbean sea, ascertained by soundings between Kingston 



(Jamaica*) and Chagres, and those between Barbados and Tobago : 



Lat. 120 00', Long. 79^ 25'— 924 fa. Lat. 12^ 10', Long. 60o 05'— 1,030 fa. 



'' no 25', " 790 30'— 969 fa. " 11° 40', " COO 10'— 1,0G0 fa. 



Taking a wide view of land shell distribution in the West Indies, it 

 may be said that the fauna of the Islands on the northern side of the 

 Caribbean sea, from Cuba to the Virgin and Anguilla banks, was derived 

 from Mexico and Central America, and that of the Islands of the eastern 

 side, from the Antigua and St. Christopher banks to Trinidad, from 

 tropical South America. It is noticeable that the mountains in the former 

 Islands, range, generally, from West to East, but in the latter from South 

 to North, excepting in Tobago and Trinidad, where they are parallel with, 

 or in the same direction as the coast mountains of the adjacent continent. 



The present geological condition of the Islands affords ample evidence 

 of the lapse of vast periods of time in the earlier tertiary epochs, during 

 which the Limestone formations, extensively developed in most of the 

 Islands, were deposited. The white Limestone of Jamaica, referred by 

 Sawkins (Geology of Jamaica, London, 1869), to the Post Pliocene, 

 covers more than three-fourths of the Island and is computed at 2000 

 feet in thickness. It rests on the yellow Limestone (Miocene), which, he 

 remarks, during the deposition of the former, "sank to grea,t depths, in 

 some places apparently 3000 feet, so as to permit the growth of those 

 great coral structures, from the debris of which the enormous calcareous 

 develoiDment of the white Limestone has been derived. The lapse of 

 time required for these important phenomena cannot be easily realized by 

 the imagination." 



That the Islands, or some of them, were formerly united and formed 

 part of an ancient continent, may, it would seem for various reasons, be 

 inferred, and the discovery of mammalian and other remains in Anguilla, 

 Sombrero, etc., is an important one. 



* The Pedro bank, within 50 miles of the southern shores of Jamaica, with an elevation of ?>(\ to 

 4(1 flithoms would give an Island 100 miles long, 3;) in breadth near its centre, and 15 at its western 

 edge. 



