A. E. Verrill—The Bermuda Islands; Geology. 117 
the deep undercutting many of the detached reefs, standing in 30 to 
40 feet of water, have a broad, flat-topped or mushroom-shaped form. 
So many of them are most undercut 20 to 30 feet below the surface 
of the sea, that it seems probable that the land remained stationary, 
or nearly so, for a long period of time, when about 30 feet higher 
than now, during the general period of subsidence. 
So, likewise, there are reasons for believing that it stood for a 
long time at about 50 feet higher than at present, owing to the 
large areas of the lagoons or sounds that lie at, or are filled up to, 
near that depth, as well as to the erosion of so many of the reefs to 
about that depth. It is not probable that the erosion of the sea 
now reaches to much more than 20 feet below low tide, with any 
degree of force. 
Figure 24.—Flats near North Rocks, at low tide. One of the men was Governor 
Lefroy. From a photograph made in 1875 by Mr. J. B. Heyl. 
All these outer reefs and many of those nearer the shores are 
overgrown with corals of various kinds, sea plumes, sea-fans and 
other gorgonians, JVillepores, serpule, mussels, Chamas, sponges, 
sea-weeds, corallines, nullipores, and many other living organisms, 
which greatly protect them from the wear of the waves, and on the 
outer parts raise the level considerably above that of the underlying 
limestone rock. Were it not for this protective covering, the reefs 
would be worn away and destroyed far more rapidly. 
Among the reef-corals* that are most efficient, both in protecting 
and building up the surfaces of the reefs, are the “brain-corals ” 
* For a fuller account and illustrations of the reef-corals and gorgonians, see 
Chapter 29. Also my articles in these Trans., xi, pp. 63-206, pls. x-xxxv; also, 
Verrill, Zodlogy of Bermuda, i, articles 11, 12, pp. 63-206 ; same plates. 
