1871.] ‘ 6 1 (Bland. 
embraced in section IY, and should add that Dentellaria does not occur in 
those Islands. Helix predominates over Buliémus in North America and 
the Islands in Sections I., I1., I1f., and 1V, while the reverse is the case 
in South America, and there is at least an increased proportionate num- 
ber of Bulimus, as compared with Helix in Section V. 
Ihave 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 my attention to a comparison of the following 
depths in the Caribbean sea, ascertained by soundings between Kingston 
(Jamaica *) and Chagres, and those between Barbados and Tobago : 
Lat. 12° 00/, Long. 79° 25/—924 fa. Lat. 12° 10/, Long. 60° 05/—1, 080 fa. 
 H1925/; 790 BORO G Oar SE TIO OM: Ee eg OO ALIC 060 fat 
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 
Jaribbean 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 divection 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 great depths, in 
some places apparently 8000 feet, so as to permit the growth of those 
great coral structures, from the débris of which the enormous calcareous 
development 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 
nferred, 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 30 to 
40 fathoms would give an Island 100 miles long, 30 in breadth near its centre, and 45 at its western 
edge. 
