150 
THE VOYAGE OF H.M.S. CHALLENGER. 
wiiid-bornc particles, carried by the Harmattan and other winds from the coast of Africa. 
The Red Clay found in the greater depths was almost entirely composed of amorphous 
and clayey matter and fine mineral particles not exceeding 0’05 mm. in diameter. In the 
dredging on the 7th March in 2435 fathoms, there were several round compact manganese 
nodules, several millimetres in diameter, and three or four sharks’ teeth coated with 
peroxide of manganese. 
With reference to the distribution of the deposits in this section the Red Clays occupy 
two areas of the ocean bottom, one to the east and one to the westwards, separated by an 
elevated area known as the Dolphin Rise, covered with Globigerina Ooze. A general 
idea of this section, with the relation of the percentage of carbonate of lime to depth and 
the distribution of the deposits, can be formed from Diagram 1. 
Off Sombrero Island . — Three soundings were taken ojff Sombrero Island, in 450 to 
590 fathoms (see Chart 7). These were designated Pteropod Oozes, for, although 
containing a large percentage of pelagic and other Foraminifera, there was also present a 
relatively large number of Pteropod and Heteropod shells. The average percentage of 
carbonate of lime was 84 •27. The mineral particles were similar in quality and quantity 
to those in the deposit in 1420 fathoms in the preceding section. 
St. Thomas to Bermuda . — In the section from St. Thomas to Bermuda (see Charts 6 
and 7), the deposits at the depths of 625 and 390 fathoms on the plateau to the north 
of the Virgin Islands were Pteropod Oozes, with 69 and 74 per cent, of carbonate of lime, 
containing a few small mineral particles and some amorphous matter. These deposits 
resemble in most respects the deposits in similar depths off Sombrero, and, although 
named Pteropod Oozes, differ considerably from deposits bearing the same name obtained 
at greater depths far removed from dry land. The deposits from depths greater than 
2700 fathoms contained from 4 to 18 per cent, of carbonate of lime, which consisted of 
broken shells of pelagic Foraminifera ; these were mostly confined to the surface layers. 
A few inches beneath the surface the deposit showed only a very slight sign of effer- 
vescence when treated with dilute acid. There is a gradual decrease in the depth from 
2960 fathoms, north of St. Thomas, onwards to Bermuda, and the corresponding increase 
in the percentage of carbonate of lime is strikingly exemplified. At 2960 fathoms there 
was 3 per cent, of carbonate of lime, at 2859 fathoms there was 18 per cent., at 2700 
fathoms there was 22 per cent., at 2600 fathoms 29 per cent., at 2475 fathoms 54 per 
cent, at 2250 fathoms 70 per cent., at 1820 fathoms 82 per cent., and at 950 fathoms 
89 per cent., while the deposits immediately surrounding the island of Bermuda in some 
insLanees contained as much as 93 per cent, of carbonate of lime, the percentage being 
greater the nearer the reef and the less the depth. The mineral particles in all the 
deposits in this section were exceedingly minute, rarely exceeding 0'07 mm. in diameter, 
and consisted of fragments of pumice, felspars, magnetite, and augite. The relation of 
depth and percentage of carbonate of lime is seen at a glance Ijy referring to Diagram 2. 
