122 THE VOYAGE OF H.M.S: CHALLENGER. 



serial temperature soundings were taken (see Diagram 1 and Sheet 6). The 

 sounding line parted on one occasion, owing to the spring of the Hydra rod 

 failing to disengage the sinkers ; and on another occasion the rod when it reached 

 the surface had nearly 100 fathoms of sounding line entangled around it, owing, in all 

 probability, to the perfect stillness of the water for some considerable distance over the 

 bed of the sea, so that the quantity of line allowed to run out in excess of the depth 

 (necessary to obtain by the time intervals a proof that the bottom had been reached) 

 descended exactly on the sounding rod, and remained entangled by the last coil 

 hitching itself round the other parts before " heaving in." 



Of the fifteen dredgings five were unproductive, the dredge having come up empty 

 twice and foul thrice. One of the most successful dredgings in this section, so far as 

 procuring a large sample of the deposit from the bottom was concerned, was obtained by 

 sinking the apparatus with 3 cwt. of sinkers attached to a Hydra rod at the bottom of the 

 dredge net, the depth being 3150 fathoms. The bag came up with a large quantity of mud 

 in it. The temperature of the mud was found to be the same as the bottom temperature 

 given by the deep-sea thermometers, and some champagne was cooled by placing the 

 bottles in it. The first trawling in 1950 fathoms, the deepest up to that time attempted, 

 was unsuccessful, as the beam of the trawl, which was of fir, was broken at the bottom, 

 whilst the pressure of the water was sufficient at that depth to crush the softer parts 

 of the wood to such an extent that, when the beam was brought to the surface, the 

 knots were standing out nearly three quarters of an inch beyond the general surface of 

 the wood. 



This section (see Diagram 1) shows a remarkable rise in the bed of the Atlantic from 

 2000 to 1525 fathoms, at a point about 1G0 miles S.W. of Ferro Island (see Sheet 6). 

 This elevation, which appears to be of small extent, is probably of volcanic origin. 

 Westward of it the bed of the ocean sinks until a depth of 3150 fathoms is reached 

 1100 miles from Tenerife, after which it gradually rises to 1900 fathoms 1650 miles 

 from Tenerife, and again sinks to 3000 fathoms (which depth it retains for 200 miles, 

 until within 100 miles of Sombrero Island). In short, the soundings clearly indicate 

 the existence of depressions on each side of the section, separated from each other by 

 a gradual submarine elevation of over 1000 fathoms (6000 feet). As the United States 

 surveying vessel "Dolphin" had obtained some soundings on this elevation in 1851, 

 it was named the " Dolphin Ridge." 



The temperature of the water at the bottom was, at all depths exceeding 1800 

 fathoms, exceedingly uniform, varying only 1 0, 5, or from 35°"5 to 37°'0 ; but although 

 this range is small, it is sufficient to indicate a decided difference between the bottom 

 temperatures on the eastern and western sides of this section. For instance, the twelve 

 temperatures on and to the eastward of the Dolphin Ridge only vary half a degree, from 

 36°'5 to 37°"0, the mean being 36°"8 ; whilst the mean of the seven temperatures west of 



