32 Papers from the Marine Biological Laboratory at Tortugas. 



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

 water, extending in a northeast direction, with the Providence NE. Channel 

 and the Providence NW. Channel, leading respectively into the Atlantic 

 and the Straits of Florida, and thus it is brought into direct connection with 

 the two main divisions of the Gulf Stream. 



The soundings in this area are shown in Chart B. So far as observations 

 go there seems to be a slight but regular upward gradient from a depth of 

 1,084 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 one-fourth to one-half mile from the shore, but unfortu- 

 nately 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-pound conical iron weight) in every case was caught upon 

 what was probably some projection on a submarine cliff, and it was im- 

 possible to free it; after several such attempts and loss of sinkers, the 

 soundings were abandoned. The entrance to the Tongue by the Providence 

 NE. Channel is of steadily increasing depth up to 2,200 fathoms at its 

 junction with the still deeper water of the Atlantic; the Providence NW. 

 Channel becomes shallower at its junction with the Straits of Florida, and 

 between Great Isaac and the western end of Bahama Island is only between 

 200 and 300 fathoms in depth. 



The surface water of the Tongue of the Ocean, except along the coast of 

 Andros, is everywhere continuous with that overlying the thousands of 

 square miles of shallows forming the Great Bahama Bank and the flats 

 and cays lying to the north and west of the Exuma Islands, whereas the 

 deeper water is only connected with the outer ocean by the comparatively 

 narrow entrance between New Providence and the north of Andros, leading 

 after a turn of about 90° into the Providence NE. and NW. Channels. 



The laboratory from which this work was done was established at 

 Golding Cay, at the eastern mouth of the South Bight of Andros; this 

 position was especially suitable for the work, as by running out a few miles 

 in a direction at right angles to the coast line the middle of the Tongue of 

 the Ocean could soon be reached, and also the mud flats to the west of the 

 island were readily accessible by water, as the South Bight runs right 

 through the island to the west coast. In this region the tides are not 

 strong, the average rise and fall being from 2 to 3 feet. 



Much difficulty was experienced in getting any definite information as 

 to the set of currents in the Tongue. Our local pilot stated that a current 

 would set in a southerly direction for weeks at a time, and then without 

 any apparent reason or change of wind would reverse and set in a northerly 

 direction for several weeks; but such information derived from the negro 

 natives can not be relied on. When taking observations on May 8, May 11, 

 and May 23, we experienced a distinct southerly drift on each occasion, 



