910 
THE VOYAGE OF H.M.S. CHALLENGER 
fathoms, but it s quite possible that less depths may be found in other places. The 
deepest cast, 2050 fathoms, was obtained in October 1873, 50 miles north of Tristan Island. 
The bottom temperature in this section varied with the depth from 36° at 2050 
fathoms to 40°'3 at 425 fathoms. The surface temperature increased from 64° on the 
38th parallel to 80° at Ascension. 
The serial temperatures showed that the isotherm of 40° occupied a mean depth of 
450 fathoms, whilst those of 45°, 50°, and 55° were all lower 200 to 300 miles north of 
Tristan Island than they were at Ascension. 
The general direction of the surface current was W.S.W. 14 miles per day. 
The following anemometer observations were taken between Monte Video and 
Ascension : — 
Date. 
1876. 
Station, 
Velocity of Wind in Miles 
per Hour. 
Force of "Wind by 
Beaufort’s Scale, as noted 
in Log. 
March 9 
331 
23 
4-5 
„ 16 
335 
20 
4-5 
„ 24 
340 
16-5 
3-4 
The albatross and other southern birds followed the ship till the 16th March when in 
lat. 32° 24' S., after which they were not again seen. 1 
In 1900 fathoms, off the mouth of the Rio de la Plata, the deposit was a blue mud 
containing about 5 per cent, of carbonate of lime, which consisted chiefly of a few shells of 
pelagic Foraminifera. The six following soundings showed depths ranging between 2650 
and 2900 fathoms. In none of these did the deposit contain any carbonate of lime, and 
no remains of calcareous organisms were observed. The remains of siliceous organisms 
made up from 15 to 20 per cent, of the deposits. The mineral particles had a mean 
diameter of 0'1 mm. or less, and consisted of fragments of quartz, plagioclase, augite, 
grains of magnetite, mica, and a very large number of fragments of pumice and volcanic 
scoriae. The fragments making up these deposits appear to have been mostly derived 
from the Rio de la Plata, whose influence on the deposits could be distinctly traced 
several hundred miles seawards. 
When the depth diminished as the Tristan plateau was reached, the character of 
1 A number of external parasites obtained from Diomeclea exulcms in the South Atlantic and South Pacific Oceans 
were sent to Mr. W. F. Kirby of the British Museum for determination ; he found the following species among them : — 
Docophorus dentut vs, Gieb., Atlantic and Pacific ; Docoplioroides brevis, Burin., Atlantic and Pacific (a very widely ranging 
species, and one of the largest of the Mallophaga) ; Lipeurus clypeatus, Gieb., Atlantic ; Nirmus angulicollis, Gieb., Pacific 
Colpnceplmhm. sp. (1), Atlantic, 
