CHAP. IV.] ST. THOMAS TO BERMUDAS. 291 
Some native plants, which form a peculiar vegetation, sending 
out enormously long runners or roots—such as /pomca pes- 
capre and Coccoloba uvifera, and the erab-grass, Agrostis Vir- 
gunica, Which is said to have been introduced, but which is now 
among the most valuable pasture-grasses on the islands—then 
take hold of it, and it becomes permanently fixed. The outer 
aspect of the sand-hill of course slopes downward toward the 
sea, and whenever its progress landward—its growth—has been 
arrested, the tendency of the incoherent mass is to travel back 
again by gravitation and the action of rain: accordingly, it is 
not unusual to be told that one of these coudées is gradually dis- 
appearing. 
The process by which the free coral-sand is converted into 
limestone is sufficiently simple, and involves no great lapse of 
time. The sand consists almost entirely of carbonate of lime 
in a state of fine ultimate subdivision, owing to its having en- 
