124 



HA RD WICKE'S SCIENCE- G OS SI P. 



THE REEF OFF PERNAMBUCO. 



A FEW remarks concerning the wonderful reef 

 ii which forms the natural breakwater and 

 harbour of Pernambuco may be interesting to the 

 readers of Science-Gossip. 



Pernambuco is an important seaport on the coast 

 of Brazil, and consists of three portions, Recife on the 

 sea border, San Antonio on an island, and Boa Vista ; 

 these are connected by bridges over the rivers 

 Caparibe and Berberibe, which debouch here. It is 

 not too much to say that this town owes its very 

 existence to the presence of this hardened sandbank 

 lying off its front. 



All up and down the coast of Brazil, from Cape St. 

 Roque to the Abrolhos, extends more or less a chain 

 of sand and mud banks parallel, and a short distance 

 off the coast ; in some places, as off Pernambuco, being 



which, however, only penetrate to a short distance, and 

 all over are little pools and tunnels only a few inches 

 deep, but forming all sorts of little nooks and corners. 

 The surface is extremely hard : fairly ringing when 

 struck with a hammer, and standing up in sharp 

 jagged points and knife-like edges, which are often 

 covered with acorn-shells. The hardness of the 

 sandstone rock of which the surface is entirely 

 composed is due to the cementing of the particles 

 together by the lime solution from the corals and 

 shell-fish, etc. Borings taken in many places reveal 

 the fact that the reef is made up of layers of sand, 

 blue mud, broken shells and gravel, which are 

 deposited in various thicknesses. While on the steep 

 river edge there is very little life except minute 

 hermit crabs, on the top and seaward side it is fairly 

 alive with lovely fish, corals, echinoderms and green 

 seaweeds. The most common fish is a species of 



Fig. 73. — The Reef off Pernambuco. 



just awash at high water, and in other places much 

 broken up, and under water all the time. The top 

 of these reefs is the home of innumerable lime- 

 secreting animals, chiefly corals and shell-fish. But 

 in no place, probably, does the reef obtain such 

 proportions as off Pernambuco. Here it has an 

 unbroken length of I3 miles, with an average breadth 

 of about 35 yards, which at high spring tides is just 

 awash. On the end at the entrance into the harbour 

 is situated an old Dutch fort and a lighthouse, and 

 for a short distance in from these the reef has been 

 built up with bricks. The top of the reef is fiat, 

 sloping down gradually to seaward, and abruptly on 

 the inshore side, chiefly due to the scouring action of 

 the rivers, which in some places have undermined the 

 banks very much, causing huge pieces to crack off; 

 this continually going on will gradually wear the reef 

 away, unless steps are taken to check this action. 

 On the top of the reef very long cracks may be seen, 



goby, which throngs all the pools, and when closely 

 pursued will make astonishing leaps and bounds from 

 one pool to another over the surface of the reef; there 

 are also several kinds of lovely coral fishes which live 

 well in an aquarium, some I had becoming so tame 

 that they would take little shrimps from my fingers. 

 The seaward edge just above low-water mark is 

 honeycombed in all directions by short thin-spined 

 sea-urchins of a dark-brown colour, while in every 

 pool are specimens of astrea corals, chiefly a brown 

 and a green variety, but in no case are they so 

 plentiful as to form an important factor in the growth 

 or maintenance of the reef. I am told, though, that 

 at Maceio — a short distance clown the coast, where 

 there is a somewhat similar reef — the corals are very 

 abundant and do form an important factor in the 

 maintenance and increase of the reef. One thing that 

 is very striking on the reef, is that the water in the 

 pools is often raised to a high temperature by the 



