CORALS AND CORAL REEFS — VAUGHAN. 219 



these algae obtained by decalcifying a specimen of the coral Orbi- 

 cella cavernosa; figure 2 shows the algae in place in the skeleton of 

 Orbicella annularis; while plate 32, figure 1, represents an oolite 

 grain in which there are no algae, but I am confident I could have 

 found an oolite grain with algae in it. 



Some of the oolite of the Bahamas remains as it was bedded in 

 the sea, except that it has risen or fallen with the movements of 

 the crust of the earth, while other rock has been broken up and has 

 supplied grains to be heaped into dunes by the winds. 



Although the Bahamas have been called coral islands, they are not 

 coral islands, for they are mostly composed of oolite formed from 

 calcium carbonate organically or inorganically precipitated in the 

 ocean, some of which has been broken up and blown about by the 

 wind. There are coral reefs in the Bahamas, and they are exceed- 

 ingly dangerous to navigation, but they occupy an area probably 

 between only one three-thousandth and one six-thousandth as large 

 as that underlain by the oolitic limestone. 



Oolitic limestone similar to that so widespread in the Bahamas 

 also occurs in southern Florida, where the area underlain by it is 

 many times greater than that occupied by coral-reef rock; and the 

 Bermudas, popularly thought to be "coral islands," according to 

 Verrill, are mostly composed of shell sand and not coral sand. Be- 

 sides these two kinds of limestone, rock predominantly composed of 

 the tests of Foraminifera and Bryozoa should be definitely excluded 

 from the category of " coral rock." The study of the formation and 

 classification of limestones is fascinating, and I should like to pay 

 much more attention to it than is practicable in the present brief 

 review of a large subject. 



I also regret being obliged to pass over, almost without mention, 

 other organisms than stony corals that contribute material incor- 

 porated in reefs. There are the discoid Orbitolites and flat-coiled 

 Orbiculina, Foraminifera so abundant in Florida and the West In- 

 dies, the stellate Tinoporus baculatus of Australia and other species 

 that live on the Pacific reefs, and Polytrema mineaceum, ubiquitous 

 on coral reefs as blood red, reticulated incrustations on dead corals 

 and shells. Alcyonaria are important contributors to bottom deposits 

 in places, although, in my opinion, no quantitative evaluation of their 

 work has yet been accomplished; and echinoids add their tests and 

 spines to the remains of the members of the other groups. Coralline 

 algae vie with stony corals in relative importance, in some places one 

 group, in other places the other holding first rank as reef -builder, 

 and at least in many places in the Pacific form incrustations just 

 landward of the sea face of barriers. An account of the charms and 

 dangers or discomforts of reefs must be abbreviated practically to 

 its suppression. I will only say beware of the long, waving, pointed 



