506 G. H. DKEW. 



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 wliere the glass is scratched or roughened. 



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

 fine 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 round 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 PHYSIOGEAPHY OF 

 THE TONGUE OF THE OCEAN AND ANDROS ISLAND, 

 BAHAMAS, B.W.I. 



The position of the Tongue of the Ocean is shown in the map on 

 page 507, 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 N.N.W.-S.S.E. 

 direction, and except at its northern end it is completely surrounded 

 by shallows or by land. On the west, for about three-quarters of its 

 length, it is bounded by the coast of Andros Island ; south of Andros 

 it is separated from the 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 sliallow water of from 2 to 3 fathoms in depth, and 

 by the chain of islands and cays extending in a N.N.W. 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 



