SOME SHOAL-WATER BOTTOM SAMPLES FROM MURRAY ISLAND, 



AUSTRALIA, AND COMPARISONS OF THEM WITH SAMPLES 



FROM FLORIDA AND THE BAHAMAS. 



INTRODUCTION. 



In order to have this investigation considered in its proper relations 

 to coral reefs and their associated phenomena, I will refer to page 54 of 

 my paper on the corals from Murray, Cocos-Keeling, and Fanning Islands, 

 where it is said that "a complex of geologic processes operating in the area 

 must be studied, analyzed, and evaluated. Among these are the agencies other 

 than corals whereby calcium carbonate may be taken from the sea-water, 

 the probability of the solvent action of sea-water on calcium carbonate," 

 etc. In a previous publication^ I made the statement: 



"In order properly to evaluate corals as constructional agents, the subject 

 needs to be studied from at least five different view points, viz: (i) In dealing with 

 sediments uplifted above the sea, the quantity of material contributed by corals and 

 that contributed by other agents must be estimated and the respective proportions 

 determined; (2) in coral reef-areas, the proportion of the area covered by corals to 

 that not covered by them should be estimated; (3) the relations of coral reefs to 

 continuity and discontinuity of marginal submarine platforms must be ascertained; 

 (4) marine bottom deposits must be analyzed according to the source of the material, 

 and the percentage of the calcium carbonate contributed by the different agents 

 estimated; (5) the rate of growth of corals needs to be known, especially for the 

 light it may throw on the rate of reef formation." 



In papers already published, I have devoted special attention to topics 

 numbered i, 2, 3, and 5, and have given some consideration to topic 4.^ 



The present paper is a preliminary contribution to the study of the 

 marine bottom deposits in three coral-reef areas, viz: (i) Murray Island, 

 Australia; (2) the Bahamas; (3) southern Florida. The Murray Island speci- 

 mens were collected by Dr. A. G. Mayer. The samples from the Bahamas 

 and Florida, here described, were collected mostly by me while working in 

 association with Dr. Mayer, and have been selected, as representing certain 

 important classes of deposits, from a lot of about 200 samples. I have 

 previously discussed the calcium-carbonate sediments of these two areas in 

 several of my paperson the geology of the areas (see bibliography on pp. 61,62 

 in this volume, especially those treating of geology). Mechanical analyses 

 have been made of all samples except those obtained in 1915, and the results 

 of the chemical analyses of a selected set are here presented. The estimates 

 of the percentage of the material contributed by different agencies is in prog- 

 ress and a report containing the results of all lines of investigation will be 

 offered for publication. 



'Carnegie Inst. Wash. Year Book No. 14, p. 222, 1916. ^Op. cit., pp. 222, 223. 



239 



