ORIGIN OF THE ATOLL. 231 



broken as to admit the influence of waves and winds. Some 

 of the large atolls of the Maldives are properly atoll archi- 

 pelagos. 



The sizes of atolls offer no objection to these views, as they 

 do not exceed those of many barrier reefs. Some of the larger 

 Maldives, according to the crater theory, would require a crater 

 forty to ninety miles in diameter, with a rim made up of 

 subordinate craters. No hypothesis of such extravagance is 

 necessary. The facts all fall in with known principles, and are 

 illustrated by known and established truths, without hypotheses 

 of any kind. 



Reefs surrounded by shallow seas, gradually deepening out- 

 ward, require no different principle for their explanation from 

 reefs with abrupt depths around. The explanation of the 

 peculiarities of the Bermudas, on page 188, can now be fully 

 understood. If the original island had a high, bold mountain 

 ridge along its south-eastern front, and low sloping land for the 

 most part to the northward and westward, the result would 

 have been what we find in fact. Previous to the elevation ot 

 250 feet, indicated by the height of the hills, the shallow region 

 on the north and west of the high land (the existing reef region), 

 must have been mostly bare of living corals, because lying at 

 too great a depth. The elevation brought it near enough to 

 the surface to again become a coral plantation. This near 

 enough, in the Bermuda seas, means forty to fifty feet, for 

 soundings show that wherever the depth is seven to eight 

 fathoms the bottom is free from living corals. If the three 

 great bays. A, B, C (see map of the Bermudas, p. 183), 

 correspond to subordinate atolls, in a ring-group, then the 

 subsiding peaks of the land became the centres of annular 

 reefs ; and the two eastern of the peaks were evidently quite 

 close together. 



It is of interest to follow still further the subsidence of a 

 coral island, the earlier steps in which are illustrated in the 

 preceding figures. One. obvious result of its continuation is a 

 gradual contraction of the lagoon and diminution of the size 

 of the atoll, owing to the fact already noted, that the detritus 



