142 CORALS AND CORAL ISLANDS. 



low tide." " The northeastern part of the reef is called the 

 Recife do Lixo, that is, Reef of the lixo, a shark-like ray which is 

 furnished with large crushing teeth and frequents the reef in 

 search of shell-fish." 



The rock of the submerged coral-heads is but a loose ag- 

 gregation of corals in the position of growth, except probably, 

 in their lower portion, where the open spaces may be filled 

 with sand and fragments and all cemented together. 



The deposits of sand or coral mud over the bottom of the 

 seas outside of barrier reefs are sometimes of great extent. 

 These sands are the fine detritus which the return flow of the 

 breaker bears seaward ; and, in still deeper water, the deposits 

 should be mainly of the finest calcareous sand or mud — fit ma- 

 terial for impalpable compact limestones. The waters outside 

 of the reef, especially when moved by heavy tidal currents or 

 storms, are often milky with the coral sand ; and while the 

 coarser sand is dropped near the shores, the finer may be 

 carried for miles and distributed far out to sea. As Major 

 Hunt, in his observations on the Florida Reefs remarks, this 

 " white water " is one of the signs of proximity to a coral reef. 

 After storms, the white coral material subsides and the waters 

 become clear again. 



Mr. Jukes, who made special examinations of the Australi 

 an reef region, and others in that vicinity, in H. M. S. Fly, 

 states that in the deeper waters outside of the great barrier, 

 "and in all the neighboring East India seas, from Torres 

 Straits, north of Australia, to the Straits of Malacca, wher- 

 ever the bottom was brought up by the lead, it proved to 

 be a very fine-grained, impalpable, pale olive-green mud, 

 wholly soluble in dilute hydrochloric acid, and therefore essen- 

 tially carbonate of lime. The substance, when dried, looked 

 much like chalk, excepting in its greener tinge. How far this 



