REPOKT ON THE DEEP-SEA DEPOSITS. 
157 
containing, along with fine amorphous matter, all the above-mentioned minerals and 
organisms. 
Bahia to Tristan da Cunha. — Between the coast of America and Tristan da Cunha 
(see Chart 16 and Diagram 6) the greatest depth obtained was 2350 fathoms. There 
were many indications of an extensive plateau surrounding the Tristan group, with depths 
varying from 1425 to 2000 fathoms. 
The deposits in depths less than 2100 fathoms on the Tristan plateau, except when 
close to the islands, contained from 85 to 95 per cent, of carbonate of lime, which was 
almost wholly composed of the shells of pelagic organisms. The three soundings in 
depths greater than 2100 fathoms towards the American coast contained from 35 to 55 
per cent, of carbonate of lime. The deposit was a Globigerina Ooze throughout the 
section. The carbonate of lime came from pelagic Foraminifera, but it was observed that 
as the ship proceeded southward the Foraminifera in the deposits became dwarfed, and 
some tropical species disappeared. There were quartz fragments in the deposits near the 
American shores, but these disappeared or were exceedingly rare in the deposits towards 
the centre of the South Atlantic. The mineral particles were very few and very small, 
never exceeding 1 per cent, and a mean diameter of O'lO mm. 
Around the Tristan da Cunha Islands. — Many hauls of the dredge and trawl were 
taken around and between the islands of the Tristan da Cunha group (see Chart 17) in 
depths of 60 to 1100 fathoms. There was generally a coarse shelly bottom, composed of 
fragments of Polyzoa, Lamellibranch and Casteropod shells, Brachiopods, Echinoderms, 
Pteropods, Serpula, and a few pelagic and other Foraminifera. In 360 fathoms close to 
Tristan the deposit was a Volcanic Sand composed essentially of mineral particles, with 
about 7 per cent, of carbonate of lime. The minerals were exclusively of volcanic origin, 
and had a mean diameter of 0'5 mm. Mineral particles of the same nature but smaller 
were present in the shelly bottoms around Nightingale Island. 
Tristan da Cunha to Cape of Good Hope. — Between the Tristan plateau and the 
Cape of Cood Hope there is a wide and deep depression (see Chart 16 and Diagram 6), 
where depths of 2550 and 2650 fathoms were obtained. The deposits at these depths 
contained 35 and 26 per cent, of carbonate of lime, consisting of pelagic Foraminifera and 
their broken parts. The mineral particles consisted of rounded and angular fragments of 
quartz, orthoclase, hornblende, tourmaline, and augite. These mineral fragments, a few 
of which were fully 1 mm. in diameter, indicate that these soundings are within the area 
which is occasionally affected with Antarctic ice. The two soundings in 2325 and 1250 
fathoms, near the coast of Africa, contained 47 and 50 per cent, of carbonate of lime. 
The mineral particles seldom exceeded 0‘15 mm. in diameter, and consisted of quartz, 
glauconite, felspar, augite, and magnetite. About 1 per cent, of these deposits was made 
up of Eadiolaria, Diatoms, and Sponge spicules ; glauconitic casts were observed after 
treatment with dilute acid, but these were not in sufficient abundance to warrant the 
