THE BERMUDA ISLANDS. 221 
David’s Head, shallow; and h, Hog-fish cut. The reef- 
grounds, inside, are encumbered with countless clumps of 
corals and coral-heads, one to four fathoms under water, with 
intervals between of five to ten fathoms; some large tracts 
are without corals, and these have a nearly uniform depth of 
seven or eight fathoms. To a vessel entering, the positions 
of the coral clumps are made known by the brownish or dis- 
colored water above them. The bottom, over large areas, is 
a calcareous clay or mud; that of Murray Anchorage, a fine 
chalky clay. 
Serpule have made large accumulations over parts of the 
reef, as stated by Nelson. ‘The tubes are so heaped over one 
another as to make rings or atoll-like elevations two feet or 
so high and two to twenty feet wide. Nelson calls them 
“Serpuline reefs.’ The reefs on the east and south sides 
are narrow, not over a fourth of a mile wide, and the waters 
abruptly deepen; we may consequently conclude that this 
southeastern side of the original land was bold and _ high, 
while off to the north and west the surface was relatively 
low and flat. 
The rock of the surface is a calcareous sand-rock of wind- 
drift and beach origin like that of the Florida and Bahama 
reefs. Prof. Wm. N. Rice says that no true coral-reef rock 
is seen anywhere above the sea-level, and that the beach and 
wind-drift formations graduate into one another and are not 
easily distinguishable. The beach-made rock is in some 
places eight to fifteen feet above tide-level. Professor Rice 
says further : ' — 
“The beach-rock is, on the average, more perfectly consoli- 
dated than the drift-rock, but in this character both rocks 
vary widely. Drift-rock, when submerged by a subsidence 
} Rice, Bulletin No. 25, United States National Museum, 1884, pp. 10, 11, 14, 15. 
