STRUCTURE OF CORAL REEFS. eI 
out any attempt at accuracy of position. The patches of reef 
in the view are of this coral-head kind, though not all as slen- 
derly supported as that above described. A vessel is represent- 
ed passing through a passage between two of them. Prof. 
Hartt, after describing the fringing reefs of the Abrolhos, gives 
the following account of the outside coral formations (p. 199). 
“Corals grow over the bottom in small patches, 7n the open sea, 
and, without spreading much, often rise to a height of forty or 
fifty or more feet, like towers, and sometimes attain the level 
of low water, forming what are called on the Brazilian coast 
chapeiroes (signifying big hats). At the top these are usually 
very irregular, and sometimes spread out like mushrooms, or, 
as the fishermen say, like umbrellas. Some of these chapei- 
rdes are only a few feet in diameter. A few miles to the east- 
ward of the Abrolhos is an area, with a length of nine to ten 
and in some places a breadth of four miles, over which these 
structures grow abundantly, forming the well known Parcel 
dos Abrolhos, on which so many vessels have been wrecked.” 
‘“‘ Among these chapeirdes I measured a depth of sixteen to 
twenty metres, and once, while becalmed, I found twenty me- 
tres alongside of one and three metres on top. They are 
rarely laid bare by the tide. They do not coalesce here to 
form large reefs as they do to the west of the islands. * * * 
Sometimes vessels striking heavily on small chapeirdes, break 
them off and escape without injury, as has been remarked by 
Mouchez. At other times a vessel may run upon one and stick 
fast by the middle of the keel, to the amazement of the cap- 
tain, who finds deep water all around, the vessel being perched 
on the chapeirges like a weather-cock on the top of a tower.” 
“In the northern part of the Parcel the chapeirées so close- 
ly unite as to form an immense reef, which has grown upward 
to a level a little above low water, and is quite uncovered at 
