On the Precipitation oj Calcium Carbonate. 41 



above this depth they are higher, and differ from them and the open ocean 

 north of the belt of calms, in the absence of a temperature thermocHne, and 

 in the maximum salinity being found below the surface. The latter points 

 either to a considerable local supply of fresh water or to a current of lower 

 salinity from either the Florida stream or the region of equatorial calms. 

 Unfortunately we have no reliable salinity observations for the two latter. 

 With regard to the accuracy of the work, Mr. Matthews makes the 

 following remarks: 



THE ACCURACY OF THE OBSERVATIONS. 



a. Salinity. — The method of taking the samples from the water-bottle was rather incon- 



venient, as a siphon was used; the samples were very small, but well pre- 

 served. The water-bottle itself might have leaked or closed at the wrong 

 depth, as was the case with earlier models.^ That this was not so is shown by 

 (i) The sharp fall in the number of bacteria at between 200 and 300 fathoms. 



(2) The close agreement of the salinities at 400 fathoms, the greatest depth at which 



they were taken on both stations. Station I gave 35.37; Station II, 35.34. 



(3) The close agreement between the bottom salinity at Station I, 34.98 at 822 fathoms, 



and the salinity found at the same depth at the nearest position at which we 

 have modern observations — i. e., Michael Sars Station 65, in 37° 12' N., 48° 

 30' W., June 1910; according to the curve this is about 34.96. 



b. Temperatures. — The National Physical Laboratory correction was given to 0.1° only, 



but the readings below 15° are comparable among themselves to 0.05° or 

 possibly less. The curv^es of temperature for the two stations agree well in 

 shape below 300 fathoms, but the temperature on Station II is generally 

 slightly higher than on Station I, as a rule by an amount corresponding to a 

 difference of depth of about 20 to 25 fathoms. 



Below 200 fathoms the curves for both stations agree ver>' closely with 

 that for Michael Sars Station 64, in 34° 44' N., 47° 52' W. 



It is almost certain from the above considerations that the results are 

 only incorrect by the experimental errors in measuring the depth, in deter- 

 mining the salinity (0.01° at most), and by perhaps 0.1° C. of temperature. 



These observations are sufficient to show that the Tongue of the Ocean 

 is an area of considerable interest from a hydrographic point of view, and 

 it is much to be regretted that the continued bad weather during our stay 

 made it impossible to obtain more observations and samples. 



BACTERIAL INVESTIGATION OF THE CHALKY MUD FLATS WHICH ARE BEING 

 DEPOSITED TO THE WEST OF ANDROS ISLAND. 



Samples of the mud were taken from the western entrance of South 

 Bight (see Chart B), and from points 2 and 3 miles out from the shore; 

 practically identical results were obtained from all these localities. The 

 sample at the mouth of the bight was taken in about 4 feet of water, that 2 

 miles out in 7 feet, and that 3 miles out in 8 feet. The samples were neces- 

 sarily taken from the surface of the mud. 



I The water-botUe only failed once, at about 890 fathoms at Station II. 



