CHAP, v.] GENEUAL CONCLUSIONS. 2Y1 



occurring at Station CCCXVIII. at a depth of 125 fathoms. 

 At Station CCCXIX. the 2° C. line is at 1100 fathoms, and 

 the other isothermobaths up to 5° C. show a corresponding rise. 

 I attribute this remarkable difference between two soundings so 

 near one another to the banking of the cold water against the 

 submarine cliff by the Brazil Current. Sounding CCCXYIII. 

 seems to have fallen directly upon the " cold wall." 



At the deeper sounding (CCCXIX.) the thermometer fell, 

 for the first time in our experience in the South Atlantic, be- 

 low the freezing-point ; but the relations of this very low bot- 

 tom temjDerature will be better understood when we consider 

 the section between Montevideo and Tristan d'Acunha. 



On the line between Montevideo and Station CCCXXXV. 

 fifteen observing stations were established. The first three of 

 these, CCCXXI. to CCCXXIIL, were on the estuary of the 

 River Plate, or (CCCXXIII.) just beyond the edge of the delta 

 at its mouth ; the next seven, CCCXXXV. to CCCXXX., gave 

 a section of a wide inlet into the western trough of the South 

 Atlantic with a mean depth of 2750 fathoms ; and the remain- 

 ing five stations, CCCXXXI. to CCCXXXY., were on the cen- 

 tral rise, with an average depth of 1850 fathoms. The mean 

 bottom temperature of the seven deep soundings is — 0°'4 C, and 

 that of the five soundings on the rise -fl°-3 C. The isothermo- 

 bath of 0°"0 C, is at a depth averaging 2400 fathoms, a depth 

 which it never much exceeds except where the cold water 

 rises against the American coast, as at Stations CCCXIX. and 

 CCCXXIII. : it therefore occurs in the line of the seven deej) 

 soundings only ; and there it forms the upper limit of a mass 

 of water with a temperature below zero, 320 scpiare miles in 

 section. Perhaps the isothermobath of 1°*5C. may fairly be 

 taken as the upper limit of the very cold water ; the section of 

 the Antarctic indraught below that temperature is here about 

 800 square miles. (The transverse section of the Gulf-stream 

 is about 6 square miles. There is no volume of water at all in 



