318 



BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



here, his later discussion in his paper on the Glacial-control theory 

 may be consulted.^ Daly says: 



"Since probably not more than 5 m. to 25 m. can be allowed for tlie thickness of 

 the post-glacial calcareous veneer in the wider lagoons, the accordance of platform 

 depth for the wider lagoons and reefless banks seems clear. Their range of 60-90 m. 

 represents magnitudes of the same order as the depths computed for the Pleistocene 

 wave-formed benches." 



I have pointed out the similarity in the depths on Saba, Pedro, 

 and Rosalind banks, to those on the atoll-lagoon floors of the Pacific 

 and Indian oceans — that is, the depths are between 20 and 30 fathoms. 



.— -• ii--„-iSi 



-->«- -'ii " A 11 'W 9 8 V-'5l3 19 



13« ;,. ",i / Q,„4 Q-o ,.*... 



Z - 14 14 13 ■. 170 



29 1716 " 13 ,, " 15 :"" 



23' 14 " 13 13 W II 16 ■,,., 



21 19 19 ,J ,2 ,. ,1 13 '^ 



34 ,« . " '^ 13.,, " " ' 171*. 



^" " 13 14 16 M7 



■■ U 11 '." 



''«ii4'^ii"/,»i,^ ^.r-;?^q 



°-'13'7.'f 4 l7 4-6-f SVu-Vo-ii 



■^ ' loe^X^A'- I3ii % 



..'17,12-'^ °0 



^BRRANILLA BANS. 



■St, — 14 



zani 13 



M, -12 

 13 13 



H 15 16^ 



81^ 



Fig. 25.— Chaet op Rosalind and Saeeanilla banks. Feom U. S. hydeogeaphic chaet No. 364. 



The possibility of the formation of atoU lagoons by submarine 

 solution was ehminated in the discussion on page 250 of this paper. 

 AtoU rims are formed by constructional processes. That the greater 

 abundance and luxuriance of reef-forming organisms on the periphe- 

 ries of atolls is due mostly, if not solely, to the intolerance of such 

 organisms to sediment, is shown by certain of my experiments. If 

 the colonies are protected from sediment, the growth of corals within 

 a lagoon may exceed that of corals on the outside. 



It is my beUef that the coral reefs forming atoU rims are superposed 

 oij platforms that antedate the formation of the living reefs, and 

 which have undergone a moderate submergence in Recent geologic 



1 Amer. Acad. Arts and Sci., vol. 51, pp. 178-199, 1915- 



