142 CORALS AND CORAL ISLANDS. 
low tide.” “The northeastern part of the reef is called the, 
Recife do Lixo, that is, Reef of the /zxo, 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 Austraiia, 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 
