CHAP. IV.] ST. THOMAS TO BERMUDAS. 285 
lished by him in the Transactions of the Geological Society in 
the year 1834, calls some small circular reefs found every- 
where round the shores in the wash of the breakers, and which 
appear to be due to their agency alone, “ Serpuline reefs.” 
As I have already said, the Bermudas Islands, in common 
with most other coral islands, are formed by the raising of the 
weather edge of the reef above the level of the sea. This 
appears to be accomplished, in the first place, by the agency 
of the waves alone. Fragments, many of them with the in- 
herent power of increasing themselves and cementing them- 
selves together through the growth of the living things which 
invest them, are piled up on one another until they reach the 
highest point accessible to the sea in storms. 
The moment the ridge appears above water, a beach of coral- 
sand is formed against it. The top of the beach dries at low 
water, and the sand is blown on, first among the crevices of 
the breakwater already formed, which it widens and strength- 
ens, and then over the breakwater to the ledges and reefs be- 
yond, which it tends to raise to the surface. In this way in 
all coral seas islands have a tendency to form along the wind- 
ward edges of annular reefs. The windward island then forms 
a shelter to the leeward portion of the ring, depriving it of the 
main source of its elevation, the piling-up of fragments by the 
waves; so that on the leeward side we usually have more or 
less of the reef remaining submerged, and any passages of 
communication between the central lagoon and the outer sea. 
I have little to add to the excellent account of the geology 
of Bermudas given by General Nelson. The Bermudas of the 
present day is simply a bank of blown sand in various stages 
of consolidation. The depth of water increases round the isl- 
and with extreme rapidity. Seven miles to the north there is 
a sounding of 1375 fathoms, and about two miles farther off 
one of 1775 fathoms. To the north-east there is water of 1500 
fathoms at a distance of ten miles; to the north-west of 2100 
I.—19 
