On the Precipitation of Calcium Carbonate. 31 



almost crystalline appearance under the microscope, and were soluble in 

 dilute hydrochloric acid, with evolution of bubbles of a gas which, when the 

 operation was performed on a microscopic slide, could be completely ab- 

 sorbed by running in a solution of sodium hydrate under the cover slip. 

 Once this process of concretion has been initiated, it appears to progress 

 independently of the presence of particles which act as nuclei, and a large 

 concretion may often be found having a number of smaller concretions 

 around it, or continued into a chain of small spheres, the whole presenting 

 somewhat the arrangement shown by freely budding yeast cells. The 

 deposition of this form of calcium carbonate also takes place on the sides of 

 the flask, and more especially over any area where the glass is scratched or 

 roughened. 



From these results it would seem strongly probable that the layers of 

 fine and unorganized chalky mud found in the Marquesas Keys are being 

 precipitated by the action of the Bacterium calcis, and it would seem a 

 reasonable suggestion that similar bacterial action may have played an 

 important part in the formation of chalk and other limestone formations 

 in geologic times. The formation of semi-crystalline concretions around a 

 central nucleus at first seemed to suggest an explanation of the formation 

 of oolite grains, but a mineralogical examination, very kindly made by Dr. 

 Fred. E. Wright, showed that the concretions did not possess that laminated 

 structure characteristic of oolite grains and that their crystalline structure 

 was nearer that of calcite than aragonite. 



SOME CONSIDERATIONS ON THE PHYSIOGRAPHY OF THE TONGUE 

 OF THE OCEAN AND ANDROS ISLAND. 



The position of the Tongue of the Ocean is shown in Chart A, which 

 includes the greater part of the Bahama group and shows its position 

 relative to Florida and Cuba. The Tongue consists of a long and narrow 

 stretch of deep water, running in a NNW.-SSE. direction, and except at 

 its northern end it is completely surrounded by shallows or land. On the 

 west, for about three-fourths of its length, it is bounded by the coast of 

 Andros Island ; southwest of Andros it is separated from Santaren Channel 

 by some 60 miles of shallow water lying over the Great Bahama Bank; 

 to the south it is separated from the Old Bahama Channel by over 50 miles 

 of shallows, averaging not more than 3 fathoms in depth; to the east it is 

 separated from the deep water of Exuma Sound by from 20 to 40 miles of 

 shallow water of from 2 to 3 fathoms in depth, and by the chain of islands 

 and cays extending in a NNW. direction from Great Exuma Island. The 

 mouth of the Tongue of the Ocean lies between New Providence Island 

 on the east and the northern extremity of Andros Island on the west ; it is 

 here some 25 miles wide and it maintains this width for the greater part 

 of its length as it stretches south. Between the southern extremity of 

 Andros and Green Cay (see Chart A) it narrows to under 20 miles, but 

 south of this point it expands eastward into an almost circular terminal 

 basin of about 35 miles diameter. The total length is about 120 miles. 



