158' REPORTS ON INVESTIGATIONS AND PROJECTS. 



were under observation at the Tortugas from June 28 to July 25, and sev- 

 eral were brought to Washington and kept under observation until August 2, 

 when I left for the remainder of the summer. On July 25 additional sam- 

 ples of mud were collected in Marquesas Lagoon and carried to Washington 

 in tightly sealed Mason jars, so that they may be kept wet for a long period. 

 Incrusted bubbles were numerous in this material soon after putting it into 

 the jars. 



It appears that oolite may be formed by calcareous crusts forming around 

 embedded and confined gas-bubbles in the manner described. The large 

 collection of bottom samples and geologic specimens have not yet been ade- 

 quately studied, and until this has been done the observations on the incrus- 

 tation of the gas-bubbles and their behavior under confinement are reported 

 without attempting to make a wider theoretic application of the observed 

 phenomena.* 



[Observations on the samples of mud and the behavior of the confined, 

 incrusted gas-bubbles have been continued subsequent to writing what pre- 

 cedes. It is probable that bubbles play only a small part in the role of ooliti- 

 zation, but the phenomenon of the attraction of particles may be funda- 

 mental. Additional studies are in progress. December 7, 1912.] 



Besides the bottom deposits and the problem of the formation of oolite, 

 other geologic processes were studied, among which may be mentioned the 

 criteria for recognizing wave-built terraces and for recognizing cross-bed- 

 ding due to wave-action, evidence of submarine solution in the Tortugas, and 

 the effect of echinoids in producing silt. These subjects are a part of the 

 general program for the study of geologic processes in the Florida region. 



* Although a general review of the oolite problem should not be given in this place, 

 two important contributions to the subject by G. Linck may be cited, and two quotations 

 introduced. The first of these papers, entitled "Die Bildung der Oolithe and Rogen- 

 steine (Neues Jahrb. fiir Min., Beilage Bd. 16, pp. 495-513, 1903), contains a statement 

 of the theories on the formation of oolite and an account of some highly important 

 experiments on the chemical precipitation of calcium carbonate and the crystalline 

 form of the precipitates. Regarding spherulites of aragonite obtained in some of 

 these precipitates Linck says (pp. 509, 510) : 



"Diese Spharolithe sind nun nichts Anderes als die runden Korner der Oolithe und 

 Rogensteine. Sie bilden sich auf anorganischen Wege als spharische Concretionen 

 mit oder ohne Kern, wo und wie sie es haben konnen. In litoralen Gebieten oder in 

 der Nahe von Korallenriffen, wo die brandenden Wogen fortwahrend Sandkornchen, 

 Bruchstiickchen organogener Kalkmassen (Muscheln, Korallen, Foraminiferen, etc.) 

 in flottirender Bewegung erhalten, lagern sich die Aragonit fasern um sie an; draussen 

 auf offenem Meere oder in abgeschlossenen Seen bilden sie sich ohne Kern, oder die 

 Einzelkrystallchen von Aragonit (Algenstabchen Rothplcts) dienen als solche, oder 

 sie umschliessen organische Massen (Insecteier, Algen etc.) und auch Gasblaschen 

 konnen von ihnen iiberkrustet werden." 



In Linck's second paper, "Ueber Bildung der Oolithe und Rogensteine" (Jenaische 

 Zeitsch., Bd. 54, pp. 267-278, Taf. 24, 25, 1909), is the statement (p_. 276) : 



"Die Oolithe bestchen ursprijnglich aus einer von Kalkspat abweichenden modifica- 

 tion des Kohlensauren Kalkes (Aragonit), bei dessen Bildung organische Wesen nicht 

 direckt beteiligt sind." 



I am not prepared to discuss the role played by aragonite in the formation of oolite. 

 However, certain facts regarding the origin of the Florida and Bahama oolites may 

 be summarized : 



Vaughan (A contribution to the geologic history of the Floridian Plateau, Carnegie 

 Institution of Washington Pub. 133, pp. 135, 173-178, 1910) described deposits of chem- 

 ically precipitated calcium carbonate in southern Florida and assigned a chemical 

 origin to the Florida oolites. 



Drew (Carnegie Institution of Washington Year Book, 191 1, pp. 14CH-141) showed 

 that denitrifying bacteria are important agents in producing this precipitation. His 

 studies during 1912 were extended to the Bahama Islands (see this Year Book, pp. 

 136-144)- 



