STRUCTURE OF CORAL REEFS. 141 



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, in 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- 

 roes 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 chapeiroes 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 chapeiroes, 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 chapeiroes like a weather-cock on the top of a tower." 



"In the northern part of the Parcel the chapeiroes 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 



