IN THE FORMATION OF CORAL REEFS. 



355 



set free from disintegrated Gorgonian colonies was about 25 pounds to the 

 square yard, over an area of nearly 100 square yards. On all of the reefs, 

 except those in the most protected situations, the destruction at this time 

 was very extensive, ranging from 15 to 100 per cent. 



As heavy storms are of frequent occurrence throughout the Antillean 

 region in late summer or early autumn, it is probable that a record extend- 

 ing over any considerable period of years would show that a fair estimate of 

 the annual destruction of Gorgonians can be obtained by making an average 

 over a period containing the date of a heavy storm. The percentage of 17.22 

 as the average for five years on the reef last mentioned will, therefore, represent 

 the conditions on an unusually well-protected reef through such a period. On 

 most of the reefs about the Tortugas group, the average destruction over a 

 considerable period of years would unquestionably be considerably higher. 



Since the facies of the Gorgonian fauna on these reefs is practically 

 unchanged from year to year under average conditions, a knowledge of the 

 growth-rate of these forms affords a basis for determining the rate at which 

 the lime is built up as spicules in the tissues of Gorgonian colonies. Records 

 of the growth-rate of a considerable number of specimens of several species of 

 Gorgonians have shown that the time necessary for such colonies to reach 

 "medium" size, such as was used in making the determinations recorded 

 in table 4, is comparatively short for all of the different species. The results 

 of these records are shown in table 8. 



In almost all of the species studied the growth is most rapid during the 

 second year and becomes progressively slower from that time on. In a few 

 species, particularly in Gorgonia acerosa, growth takes place for an indefinite 

 period and there seems to be no definite size for the colony as there is for most 

 other forms. 



In relation to the stability of the facies of the Gorgonian fauna on any 

 area, it has been observed that after a period of severe destruction by storm 

 there is always an unusually large number of young colonies present on the 



