238 bulletin: museum of compakative zoology. 



ing^the general features of other calcareous reefs, being by turns hard 

 and flat, cavernous, shelly and fragile, and filled with pools of water 

 containing seaweeds and a few small corals. The part nearer the igneous 

 rocks is the more solid ; further from the shore it becomes more cavern- 

 ous, the most fragile places being where the reef has its greatest width. 

 It is higliest along the outside, where it is covered by the dark and 

 brownish polyps, seaweeds, and other calcareous growths. The pools 

 in this reef liave in them a few small corals, Siderastraea and Favia, 

 the specimens of the latter genus being the finest I have seen on 

 the Brazilian coast. The specimens of Siderastraea are small, none 

 being found larger than a man's head. It is probable tliat many of 

 the corals have been removed from this reef for the purpose of making 

 lime. 



To the oceanward of the southeastern corner of the island where the 

 fringing reef ends, the rocks are rough and are washed high up by the 

 waves, which break here with full force. Wherever the water breaks 

 over the top of oue of the high rocks at this corner of the island and 

 runs down the inside surface, this inside is covered by calcareous terraced 

 rings which grow along the sides and over the surface parallel to each 

 other like broken contour lines. These rings contain little pools of 

 water one above another, and this water is continually renewed by the 

 splashing of the waves and by spray from the ocean. These little bands 

 are about three centimetres in thickness, are from eight to thirteen cen- 

 timetres high, and are surmounted by rows of barnacles. 



The outer side of the rocks along the northeast part of the island 

 appears to be crusted over by dark-brown corallines. Near the middle 

 of the east side of the island there is a large pool among the higher 

 rocks of the shore, the water of which is continually renewed by the 

 waves ; this pool contains a few fish, corals, etc. — all quite beyond tide 

 level. It is only by leaping that the waves reach this height, but the 

 island standing so well out at sea receives the full force of the waves, 

 and they are thi'own by the huge blocks of rock at the base of the bluflf 

 high into the air, and are thus carried as spray or as waves high up the 

 sides of the rugged cliff". 



Near this large pool and supplied in the same way are two other 

 pools, one a little above and emptying into the other. The two are 

 about the same size, being about twelve metres in length by one to two 

 metres in width, and a metre or more in depth. These higher pools 

 contain excellent exhibitions of the wearing or dissolving power of the 

 sea-urchins upon rocks. The sides of the rocks are almost completely 



