No. 630] SHORTER ARTICLES AXD DISCUSSION 



were due to the erosive inroads of the sea. The collapse of 

 caves and the general scouring action of tidal and other cur- 

 rents, as subsequently emphasized by Agassiz, 4 rather than very 

 local basal subsidences, were thus regarded as the forces respon- 

 sible for the lagoons. 



So far as the general question of "coral" islands is con- 

 cerned, it is sufficient to note that, strictly speaking, Bermuda 

 is not, of course, a "coral" island at all, nor is its form that 

 characteristic of the islands commonly so termed. 5 The problem, 

 however, of this erosive action of the sea, its nature, and its role 

 in the determination of land form in the case of a limestone 

 island, is insistently presented by the enclosed lagoons to which 

 I have referred. Murray's idea of the solvent action of natural 

 waters in relation to the hollowing-out of lagoons and to the 

 building of barrier reefs has lately been attacked from several 

 aspects. Thus Mayer 6 has pointed out that at Tutuila (Samoa) 

 and at Oahu, the surface waters draining into the sea are prob- 

 ably too alkaline, and contain too much calcium derived from 

 the land, to be effective in dissolving the shoreward parts of the 

 coral reef-flat. In the case of lagoons, a great number of in- 

 fluences are at work to control the erosion of the rock and the 

 deposition and removal of silt. 7 The measurement of the al- 

 kalinity of the lagoon water provides but one of the factors 

 requisite for analysis of the thoroughly heterogeneous equilibrium 

 between the water and the limestone. Such determinations are 

 nevertheless valuable, and during a recent residence at the Ber- 

 muda Biological Station I had the opportunity of carrying out 

 estimations of this kind over a period of many months. 8 At- 

 tention was chiefly given to the alkalinity of the semi-enclosed 

 waters as compared with that of the open ocean. The determi- 

 nations were made eolorimetrically. by means of thymolsulpho- 

 nephthalein with borate standards. 3 and phenolphthalein. The 

 alkaline reserve was not estimated. 



