BOTTOM SAMPLES, MURRAY ISLAND, THE BAHAMAS, AND FLORIDA. 273 



71. 1 per cent; average of the three 60.7 per cent, a higher figure than for speci- 

 men 79, from South Bight. It was from this locahty that Drew collected 

 the samples he used in his study of the bacteria "of the chalky mud flats 

 which are being deposited to the west of Andros Island."^ Here he found 

 "160,000,000 bacteria per i c.c." He says: "The actual number in the 

 mud possibly exceeds this figure, since a large proportion of the bacteria 

 would probably settle with the larger particles after the first dilution." 

 Dr. Kellerman studied a part of specimen No. 177, which I sent him, and 

 essentially confirmed Drew's results.^ This mud is largely a bacterial pre- 

 cipitate, but, as will presently be shown, other factors which might cause 

 precipitation need to be considered. 



Drew did not sound the mud to find out how deep it is. I found the mud 

 at station 177 to be 2 feet thick over hard rock; water 6 feet deep. On the 

 west side of the channel into the west end of South Bight, the water is 2 feet 

 deep, mud 7 feet thick. Except some foraminifera and a few other small 

 organisms, bacteria are almost the only forms of life present. I searched 

 specimen 177 for Coccolithophoridae and occasionally found one. The almost 

 complete absence of these minute organisms is in contrast to their frequent 

 presence in the samples from Cocoanut Point and Murray Island. 



The percentage of MgCOs is 2.72, a figure about the same as that for 

 specimen 79 (2.56 per cent), but much lower than the one for Cocoanut Point 

 (5.24 per cent). The muds off the west side of Andros are closely similar to 

 those along South Bight. 



Some other facts of the physical conditions need consideration. Mr. 

 Dole has determined the salinity of water samples I brought back,^ and 

 found that at Station 177 to be 3.886 per cent, while two water samples at 

 Cocoanut Point had salinities of 3.64 per cent and 3.66 per cent respectively, 

 showing a distinctly higher concentration on the west than on the east side 

 of Andros Island. Drew obtained the following surface salinities in the 

 Tongue of the Ocean :^ 6 miles east of Golding Cay, 3.624 per cent; 13 miles 

 east of Golding Cay, 3.658 per cent; figures essentially the same as those 

 reported by Dole. 



Data on the surface temperatures of the water on the two sides of the 

 island are deficient. Drew reports surface temperatures of 26.90°, 26.30°, 

 27.10° C, during May, and I have some additional records, but they are 

 so fragmentary as not to be worth publishing. There are no records for 

 the west side of the island. 



The less concentration of salts in solution in the water on the east side 

 of Andros, as compared with that on the west, is to be explained by deep 

 water coming very near shore on the east side, the 50-fathom curve being 



'Carnegie Inst. Wash. Pub. No. 182, pp. 41-43, 1914. 

 'Carnegie Inst. Wash. Year Book No. 13, pp. 228-229, I9'5- 



'The results of Mr. Dole's investigations of the salinity of the Florida reef tract and of some areas in the 

 Bahamas are given in a subsequent article in this volume, pp. 299-315. 

 *0p. sup. cit., pp. 37, 38. 



