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BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



Isle of Pines the descent from the shore in 9 sea-miles is 13,080 feet, 

 a slope of about 1 in 4. The Gulf of Cazones appears to have been 

 outlined by faulting. This shelf differs from the one considered in 

 the preceding paragraph, in that the Isle of Pines, whose area is 

 about 1,200 square miles, stands on its outer margin, and apparently 

 has affected the course of the fault. However, there was here also 

 an undersea flat, which was produced by the gentle seaward tilt of 

 low-lying geologic formations, and its outer margin was also deter- 



TiG. 16.— Chart of colokados eeefs, cub a. From U. S. hydrographic chart no. 966. 



mined by faulting. The living reefs are growing on its submerged 

 unfaulted part, above which they rise as disconnected patches or as 

 a broken barrier. 



The Colorados reefs (text-fig. 16) grow as patches of barrier reefs 

 or upon a shelf, which, according to Henderson, largely consists of 

 coral rock that had been uplifted above the sea and then depressed.^ 



The conditions under which the Cuban offshore reefs are growing 

 can be very easily summarized, as follows: (1) They are superposed 



1 Henderson, John B., Cruise of the Tomas Barrera, pp. 62-64, 126-130, 1916. 



