STRUCTURE OF CORAL ISLANDS. 167 



Florida Reefs and Keys. — This region of coral formations 

 has been described by Prof M. Tuomey [A?nej'tcan Journal 

 of Science, vol. xi., 185 1), Professor Agassiz (Coast Survey 

 Reports for 185 1 and 1866, and Bull. Mus. Comp. ZooL, i., 363), 

 and Captain E. B. Hunt {A?n. J. Scl.^ xxxv., 1863). A few 

 paragraphs from the papers of the first two of these observers 

 are here cited. The map at the close of the volume illustra- 

 ting this Florida reef-region is from the Report on Deep-Sea 

 Corals of L. F. de Pourtales, published in the Illustrated Cata- 

 logue of the Museum of Comparative Zoology in 187 1. First, 

 from Professor Tuomey : — 



" Key West is about six miles in length and two m.iles wide, 

 the highest point being fifteen or twenty feet above mean tide. 

 The deepest wells are about fifteen feet in depth ; the water in 

 them, which is slightly brackish, ebbs and flows with the tide." 

 "The rock perforated in these wells, like that everywhere else 

 exposed, is suHiciently soft to yield readily to the axe, with 

 the exception of a thin crust of a few inches on the surface, 

 which is quite hard, especially where it is exposed alternately 

 to the action of the tides and atmosphere. This indurated 

 crust may be seen on the road between the town and the bar- 

 racks, and around the salt works. Below this crust the rock 

 is quite soft, and in some other respects resembles the Ala- 

 bama white limestone \ but the most striking difference next 

 to that of organic remains, consists in the distinctly oolitic 

 structure of the Florida limestone. This structure is seen 

 where one would be led to expect it, in the fine grained seams. 

 A few hundred yards from the hospital a quarry has been 

 opened where the rock may be examined. The organic re- 

 mains consist of broken shells and water-worn fragments of 

 corals, which, both in species and state of preservation, re- 

 semble those on the shores of the island. Except in degree of 

 hardness, the rock does not differ from the calcareous sands 

 thrown up by the waves on the shore in the vicinity; and 

 the conditions presented by the loose moving sands are not 

 favourable to the habits of molluscous animals, nor are fossil 

 shells very abundant in the limestone of the island. Oblique 



