264 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



Comparisons with Samples from Behind Murray Island Reef. 

 A comparison of both the mechanical and chemical analyses of the 

 Murray Island material from the southeast reef, line I, at stations 200, 600, 

 1,200, and 1,600 feet from shore, with that from Cocoanut Point reveals close 

 similarity. The following table shows the relative amounts of silt and clay 

 in both localities: 



Percentages of silt and clay in samples from Murray Island and Cocoanut Point. 



The following table gives the relative amount of MgCCV in the two sets 

 of bottom samples from behind Murray Island and Cocoanut Point reefs: 

 Percentages of MgC0 3 in samples from Murray Island and Cocoanut Point. 



The MgCCV is 0.505 per cent higher in the Murray Island sample, a 

 difference of roughly 10 per cent, when the MgC0 3 ratio of the two samples 

 is compared. 



The estimates of the percentages of the different ingredients in the 

 Cocoanut Point samples have not been completed, but it will be seen from 

 the statements on page 263 that the agencies contributing to the bottom 

 deposits in the two areas are similar, except that alcyonaria are more important 

 in the Bahaman than in the Australian material. Another similarity should 

 be indicated : Murray Island is south of the equator in the track of the south- 

 east trade winds, while Cocoanut Point lies north of the equator near the 

 northern limit of the northeast trades. In both areas the winds blow across 

 the reef. The relations are such in both areas that currents induced by 

 winds and tides tend to remove fine sediment and transport it to other areas. 

 Therefore in these two areas, on nearly opposite sides of the earth, there 

 are complexes of similar factors at work, which produce geologic results 

 essentially identical. 



'Hypothetical combination. 



