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parallel with the coast, which had its central part consolidated, 

 and then the loose matter removed by a slight change in the 

 set of the currents ; and Gardner's, that it owes its origin to 

 the decay of rock between it and the shore. 



Mrs. Graham merely repeats what seems to be the general 

 opinion of those who visit the coast without making much use 

 of their eyes; viz., that it is a coral reef — an opinion formed in 

 the absence of any careful examination, from the association 

 of ideas mariners usually attach to the term reef; viz., that 

 it is a coral formation — an opinion which Darwin distinctly 

 denies, and in which I fully coincide, although very fine speci- 

 mens of coral are obtained from outside the reef near Paraiba. 

 I have examined the structure of the reef very carefully at 

 Bahia, Maceio, Cape Sao Agostinho, Pernambuco, Paraiba, and 

 Ceara, and at each of these points found its character nearly 

 identical ; in fact, only varying with the fineness and coarse- 

 ness of the sand which composes the beach opposite to it. At 

 Bahia it is exceedingly close and compact, as shown by the 

 specimens presented; it makes good building stone, and is 

 much worked for this purpose. At Pernambuco, on the con- 

 trary, it is very porous, and makes excellent niters for the 

 impure water with which the place was formerly supplied. 



The water between the reef and the shore is navigable the 

 greater part of its distance for canoes and jangadas; and 

 between Cape Sao Eoque and Aracati, a distance of about 200 

 miles, for vessels of considerable draught of water. At this 

 part the reef lies several miles from the coast, but everywhere 

 it presents the same general appearance of a shelf of sand- 

 stone, covered more or less with coralline, sloping gently down 

 into the sea and steep on the land side. At Pernambuco it is 

 traversed in a remarkable manner by irregular fissures, which, 

 though they seem gradually to become filled up with coralline, 

 the remains of shells, and sand, afford a safe refuge for 

 numerous crustaceae and small fish. The smoothness of the 

 surface is also destroyed by the irregular accumulations of 



