CHAP. IV. ] ST. THOMAS TO BERMUDAS. 309 
tion of carbonate of lime, which is deposited as stalagmite as 
the water evaporates, and thus a ring-like crust is produced 
at a little distance from the spot where the drop falls. When 
a ring is once formed, it limits the spread of the drop, and 
determines the position of the wall bounding the little, pool 
made by the drop. The floor of the cave gradually rises by 
the accumulation of sand and travertine, and with it rise the 
walls and floor of the cup by the deposit of successive layers 
Fig. 83.—Calcareous Concretions in Aolian Rock, Bermudas. 
of stalagmite; and the stalagmite produced by the drop per- 
colating into the limestone of the floor hardens it still further, 
but in this peculiar symmetrical way. From the floor and 
sides of the cup the water oozes into the softer limestone around 
and beneath; but, as in all these limestones, it does not ooze 
indiscriminately, but follows certain more free paths. These 
become soon lined and finally blocked with stalagmite, and it 
