240 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



The investigation of the source of the material, its mechanical state, 

 and its chemical composition indicate certain classes of calcium carbonate 

 deposits, some of them divisible into grades; and it is hoped that progress 

 has been made toward outlining a method whereby an adequate classification 

 of such sediments may ultimately be achieved. The deposits must not only 

 be classified, but the areal extent of each must be determined, and, if possible, 

 the volume of each should also be estimated. 



PERCENTAGE OF INGREDIENTS ACCORDING TO SOURCE. 



Calcium-carbonate deposits are derived initially from two sources: 

 (i) through the activities of organisms which cause precipitation either 

 inside or outside their tissues; (2) through chemical precipitation, either 

 by inorganic agencies or by the activities of organisms which change the 

 chemical composition of substances in solution in the water, producing super- 

 saturation with reference to CaCOs, or which by more purely physical pro- 

 cesses may cause a state of supersaturation with reference to CaCOs. In 

 many marine sediments of to-day, in addition to that derived directly through 

 the processes indicated, material is also derived from previously formed lime- 

 stone which has been disintegrated and delivered to the sea. 



In preparing for making percentage estimates of ingredients according 

 to origin, a reliable reference collection had to be assembled. The prelimi- 

 nary working collection comprises oolitic limestones (thin sections and 

 powders); calcium carbonate bacterially and inorganically precipitated in 

 the laboratory; muds formed largely by bacterial action, although other 

 agencies may have cooperated; coccolithophoridae; thin sections and crushed 

 fragments of calcareous algae; a few radiolaria; over 100 named species and 

 crushed fragments of common foraminifera; about 500 thin sections and 

 crushed fragments of corals; mounted spicules of many species of alcyonaria; 

 thin sections and crushed fragments of echinoids, bryozoa, mollusca, and 

 Crustacea. The collection is increased as the needs of the work require it. 



Professor F. W. Clarke and Mr. W. C. Wheeler have rendered a valuable 

 scientific service by chemically analyzing the skeletons of representatives of 

 different groups of marine organisms. The completed results of the investi- 

 gation have been brought together in a paper submitted for publication and 

 entitled "The inorganic constituents of marine invertebrates and calcare- 

 ous alg£e," by F. W. Clarke and W. C. Wheeler.^ Professor Clarke has 

 kindly allowed the use of a copy of their manuscript while their paper is in 

 press. The authors have shown that the chemical composition of the 

 skeletons secreted by marine organisms varies from group to group, and 

 that in certain groups, especially echinoids and alcyonaria, there is a definite 

 relation between temperature and the ratio of MgCOs to CaCOs, the mag- 

 nesia being relatively higher in warm than in cold waters. 



These investigations have rendered possible the correlation of the chem- 

 ical composition of an entire sample with that of the various ingredients 



'U. S. Geol. Surv. Prof. Pap. No. 102, pp. 56, 1917. 



