72 A. H. Verrill—The Bermuda Islands. 484 
and often broken up into distinct patches or groups, and small 
detached heads, with deep and narrow channels between them. 
These broad nearly level reefs are locally called “ Flats.” (Fig. 27.) 
The four North Rocks, which stand on the platform of the outer 
reefs, about 8 miles north of St. George’s Island, are the only points 
that are exposed at high tide. ‘The largest of these is only about 12 
or 13 feet high, above low tide, and about 7 feet in diameter (see 
figure 30). They are, like the reefs themselves, last remnants of 
what were once islands, now destroyed by the sea. (See map, fig. 26.) 
These rocks are interesting historically, as well as geologically, for 
it was in close proximity to these that the “ Bonaventura,” with 
Henry May on board, was wrecked in 1593, as mentioned on another 
page, and so they were represented, with this wrecked vessel, on the 
reverse of the original seal of the Bermuda Company (see figure 29, 
ch. 23). They lie 12 miles N.N.W. from Catherine Point, at the 
eastern end of St. George’s Island. Mills Breaker, which is dry at 
low water, lies 6 miles N.E. from Catherine Point. (See map, fig. 
26.) 
Within the outer reefs, and between the anchorages, there are 
innumerable detached reefs and groups of reefs of various sizes and 
shapes, but often covering many square miles, where the water is so 
obstructed and filled with reefs that no vessels of any kind can pass 
through them, except small boats in pleasant weather. 
All these reefs are overgrown with corals of various kinds, sea-fans, 
serpule, mussels, 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 speedily worn away and destroyed. 
Among the reef-corals that are most efficient, both in protecting 
and building up the surfaces of the reefs, are the “ brain-corals” 
(Meandra), the “star-corals” ( Orbicella and Siderastreea); Porites ; 
and the finger-coral (Millepora alcicornis). 'The latter is very 
abundant on all the reefs and rocks, including those near the shores, 
for it grows in very shallow water. It forms large and handsome 
masses of elegantly branched fronds, dark russet-brown in color 
when living. The common brain-coral (JL labyrinthiformis) is 
exceedingly abundant, and forms thick, rounded masses, sometimes 
4 or 5 feet in diameter, orange yellow in life. The other brain-coral 
(MM. cerebrum) forms similar masses, usually light yellow or greenish 
in color, chiefly on the outer reefs. (See Part V, and plates.) 
