ORIGIN OF THE ATOLL. 269 



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 sub- 

 ordinate craters. No hypothesis of such extravagance is ne- 

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

 illustrated by known and established truths, without hypo- 

 theses of any kind. 



Reefs surrounded by shallow seas, gradually deepening 

 outward, require no different principle for their explanation 

 from reefs with abrupt depths around. The explanation of 

 the peculiarities of the Bermudas, on page 221, can now be 

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

 mountain ridge along its southeastern 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 of 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 liv- 

 ing 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 eh»ht fathoms the bottom is free from living corals. 

 If the three great bays, A, B, C (see map of the Bermudas, 

 p. 218), 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 evidentty 

 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 



