326 NATURAL SCIENCE. Nov., 



and 1893 respectively. In the course of these surveys special atten- 

 tion was paid to the biological conditions of the bank, in order to 

 throw light on the general question of reef- and atoll-formation. 

 The scientific portion of the work was fortunately superintended by 

 Mr. P. W. Bassett-Smith, surgeon, R.N., and the three reports that 

 he sent home have now been published together[by H.M. Stationery 

 Office, with a preface by the Hydrographer. 



" The general result of the whole examination," says Captain 

 Wharton, "may be stated to be that on the whole of the 200 miles 

 forming the periphery of the bank there exists a rim [of coral in 

 luxurious growth, and at a remarkably even depth below the surface 

 of from 9 to 14 fathoms, this rim being broken here and there by 

 passages of greater depth, but less than the general depths of from 

 40 to 48 fathoms which prevail over the whole central body of the 

 bank. On one spot only on the rim was a depth of as little as 

 6|- fathoms found, and on a patch in the centre of the lagoon, a small 

 spot of 5 fathoms, the shoalest water on the whole bank was found. 

 This evenness of depth is the most striking feature of the chart, and 

 when the great distances are considered, this appears to be a strong 

 argument against any movement of the bottom since the atoll form 

 was assumed. It is at any rate quite evident that from the present 

 time onwards no movement is necessary in order to form in the future 

 a perfect atoll, the simple growth of the coral on the rim sufficing ; 

 and that we may have here an instance of a suitable original founda- 

 tion for an atoll so formed, as pointed out by Mr. Darwin." 



Confirmation of the above opinion will also be found in the 

 reports of Mr. Bassett-Smith himself. Thus, he says, " there appears 

 to me no evidence of either subsidence or elevation of this reef other 

 than that brought about by the building up on a submarine mound of 

 both living and dead forms of calcareous secreting organisms from the 

 animal and vegetable kingdom." And again : " Altogether forty-one 

 genera of corals were represented, excluding the alcyonarian and 

 hydroid corals, viz., Tubipora, MiUepora, Stylaster, and Distichopora, 

 giving a total of twenty-nine genera in depths between 25 — 35 

 fathoms, and twenty-seven in over 35 fathoms ; but out of these 

 several cannot fairly be called reef-building, as Lcptoseris, Psammocora, 

 Anacropora, and Balanophyllia, with Cycloseris and other simple corals. 

 With these facts before us there can be no reason to doubt that the 

 actual increase of solid calcareous rock from these marine organisms 

 requires a much less narrow limit of depth than is usually assigned to 

 them, and helps very materially to explain the great depths of these 

 lagoons, which has been up to the present time one of the most 

 vexed questions with regard to the formation of these atolls, 

 and one of the strongest points in support of Darwin's theory. 

 Together with these growing corals in 30 — 50 fathoms (as pointed out 

 before) exists an enormous amount of rock formed by calcareous 

 algae in situ, and probably the coating on the surface of the living 



