182 THE VOYAGE OF H.M.S. CHALLENGER. 



The bottom temperature at depths exceeding 1800 fathoms was again remarkably 

 uniform, varying only o, 2, the mean being 36°"5 and the extremes 36°"4 and 36°"6. 



The serial temperatures of this section showed some peculiarities, which, from pre- 

 vious experience, had not been expected. Up to this time the isothermal lines had run 

 fairly parallel with the surface, no matter whether proceeding in an east and west, or 

 north and south direction, unless some disturbing cause, such as the Labrador Current, 

 interfered to prevent their doing so ; but, in this section, the lower isotherms all rose 

 towards the south. Thus, the isotherm of 40° maintained an average depth of 950 

 fathoms for 450 miles from Madeira, and then rose gradually, though somewhat irregularly, 

 to 800 fathoms at St. Vincent. The isotherm of 45° rose irregularly from a depth of 

 700 fathoms at Madeira to 380 fathoms at St. Vincent ; and the isotherm of 50° 

 rose from 420 fathoms at Madeira to 200 fathoms at St. Vincent. The isotherms above 

 50° were nearly parallel with the surface. 



No regular current observations were taken on the passage to St. Vincent, but it was 

 noticed, whilst dredging under the lee of Palma Island, that the surface water was run- 

 ning to the northward, at an estimated rate of one mile per hour, and on the 26th July, 

 at Station 92, it again had a northerly tendency. 



On the 18th July, at Station 84, the velocity of the wind was 22 miles per hour by 

 the anemometer, its force being registered as from 5 to 6. 



At 11 p.m. on the 26th July the island of San Antonio was sighted, and the ship 

 stood off for the night. On the 27th, as soon as the fog cleared off the land, a line 

 of soundings was carried into the channel between the islands of St. Vincent and San 

 Antonio (see Sheet 11), and the ship anchored in Porto Grande at 4.30 p.m. 



The deposit to the west of the island of Palma in 1125 fathoms was a brown volcanic 

 mud, containing about 6 per cent, of carbonate of lime. The size of the mineral particles 

 rarely exceeded 0"25 mm. When the mud was passed through sieves the washings which 

 remained were almost wholly made up of dead shells of Pteropods and Heteropods. In 

 the dredge there were a few animals and several large fragments of a dead Gorgonoid Coral 

 (Corallium), coated with manganese peroxide, similar to that obtained in 1525 fathoms 

 about 200 miles further south on the Tenerife-Sombrero section (see page 125). The next 

 sounding was in 2300 fathoms, a little to the west of the position where the depth of 1525 

 fathoms just referred to was observed in February. Here the deposit was a Globigerina 

 ooze, containing 57 per cent, of carbonate of lime. Later on the same day, 21st July, a 

 sounding and dredging were obtained in 1675 fathoms, on the same hard ground with dead 

 coral, and in nearly the same position as in February, when the dredge brought up more of 

 the black coral, fragments of a Polyzoon (Nellia simplex), one specimen of Ophiomusium 

 pulchellum, one of Ophiomitra carduus, and two Peneid Shrimps. In 2300 and 2400 

 fathoms farther south a Globigerina ooze with 64 and 58 per cent, of carbonate of lime 

 was obtained, containing no Pteropod or Heteropod shells. The mineral particles were 



