THE PRECiriTATION OF CALCIUM CARBONATE IN THE SEA. 507 



as it stretches south. Between the southern extremity of Andros 

 and Green Cay it narrows to under 20 miles, but south of this point 

 it expands eastwards into an ahuost circular terminal basin of about 

 'Ao miles diameter. The total length is about 120 miles. 



Fi(;. 1. — Slap showing position of the Tongue of the Ocean. The dotted line shows the 

 100-fathom line ; in most parts this almost coincides with the 5-fathom line. 



To the north, the Tongue is connected by a stretch of deep water 

 extending in a N.E. direction, with the Providence N.E. Channel, and 

 the Providence N.W. Channel, leading respectively into the Atlantic 

 and the Straits of Florida, and thus the Tongue of the Ocean is 

 brought into direct connection with the two main divisions of the 

 Gulf Stream. 



The soundings in this area show a slight but regular upward 

 gradient from a depth of 1084 fathoms at the mouth, to 740 fathoms 

 in the southern terminal basin. Along the margins the gradient is 

 extremely steep, and along the coast of Andros our observations showed 

 that it was almost perpendicular at a distance of from a quarter to 

 half a mile from the shore, but unfortunately no complete observations 

 have been made from which this gradient could be calculated. When 

 attempting to make soundings in this area, the sinker (a 30-lb. conical 

 iron weight) in every case was caught upon what was probably some 

 projection on a submarine cliff, and it was impossible to free it ; after 

 several such attempts and loss of sinkers the soundings were 

 abandoned. The entrance to the Tongue by the Providence N.E. 



