ORIGIN OF BARRIER REEFS AND ATOLLS. ahh 
writer has since said, that perhaps the coral rock encases a 
voleanic mountain ; another has gone further and dropped the 
perhaps. But these statements are at present unwarranted. 
On Cuba, according to Prof. W. O. Crosby,’ coral rock 
occurs in successive terraces up to a height of nearly 2,000 
feet, and, excepting small breaks, makes the circuit of the 
island. The terraces are described as a striking feature in 
the view from the water. One terrace-plain, at 30 feet ele- 
vation, is in places nearly a mile wide and extends almost 
horizontally for hundreds of miles. <A second, of 200 to 250 
feet, rises steeply from the imner edge of the first, and a , 
third reaches a level of 500 feet. Near Havana the eleva“ 
tion is over 1,200 feet, and the rock, as reported by Mr. A. 
Agassiz, is true reef-rock. The mountain El Yunque, five 
miles west of Baracoa, 1,800 feet in height, is_volcanic rock 
below, but coral for the upper 1,000 feet. Further coral lime- 
stone has been found by Mr. Sawkins, on J amaica, at a height 
of 2,000 feet. “My. Crosby concludes that the great thickness 
of the now elevated reefs could have been produced only 
“ during a progressing subsidence,’ so that “we have appar- 
ently no recourse but to accept Darwin’s theory.” 
We are thus led to the conclusion that each coral atoll ~~ ‘\ 
once formed a fringing reef around a high island. The 
fringing reef, as the island subsided, became a barrier reef, 
which continued its growth while the land was slowly dis- 
appearing. The area of waters within finally contained the 
last sinking peak. Another period, and this had gone, leay- 
ing only the barrier at the surface and an islet or two of 
coral in the enclosed lagoon. Thus the coral wreath en- 
circling the lofty island becomes afterward its monument, 
and a record of its past existence. The Paumotu Archi- 
1 Proceedings of the Boston Society of Natural History, 1882-1883, xxii. 124. 
