THE VOYAGE OF H.M.S. CHALLENGER. 
15() 
cent. This is a good instance illustrating the diminution of carbonate of lime in the deposit 
with increasing depth, as here the surface conditions were the same, and the character of 
the mineral particles alike in all the soundings. The mineral particles consisted of 
felspai-s, hornblende, augite, magnetite, and vitreous particles. Radiolaria, Diatoms, and 
fragments of other siliceous organisms did not make up more than 1 per cent, of the 
deposits. 
Ofi’ Fernando Noronha. — At Fernando Noronha (see Chart 14) dredgings were taken 
close to shore, in depths varying from 7 to 25 fathoms. The bottom was covered with a 
calcareous sand or gravel, of a mottled red and white colour, the fragments varying from 
2 to 3 cm. in diameter, and consisting chiefly of calcareous Algae, with fragments of 
Echinodenns, Molluscs, Polyzoa, Corals, Polytrema, Amphistegina, and other Foramini- 
fera. There were also numerous volcanic pebbles. 
Fernando Noronha to Pernambuco and Bahia . — Between Fernando Noronha and 
the American coast there is a deep depression, in which a depth of 2275 fathoms was 
obtained, and comparatively deep water extends to within 30 miles of the American 
shore. With one exception, the deposits in the section from Fernando Noronha to Per- 
nambuco (see Charts 12 and 15) were Globigerina Oozes, with from 37 to 80 per cent, of 
carbonate of lime. The exception was a Ked Mud from 500 fathoms, the first of the kind 
obtained since leaving England. 
The deposits along the coast of Brazil difiered in colour from those which the 
Challenger found along other continental shores. Here they were red, due, apparently 
to the large quantities of ochreous matter carried into the sea by the Brazilian rivers. 
Usually the colour of deposits along continental shores is blue, with a surface layer of a 
red or brownish colour. The carbonate of lime in the soundings off this coast varied from 
60 to 6 per cent, according to depth, distance from the coast, and whether or not opposite 
the embouchures of rivers. The mineral particles consisted of fragments of quartz, 
plagiocla.se, felspars, sometimes kaolinized, epidote, mica, augite, hornblende, fragments 
of rocks and vitreous particles, the size varying from 0'05 to 1 or 2 mm. in diameter. 
Radiolaria and Diatoms were nearly, if not quite, absent from these deposits, and when 
]>rescnt they, along with siliceous Sponge spicules, did not appear to make up over 1 per 
cent, of the whole deposit. The apparently complete absence of glauconite along this 
coast was also remarkable. 
If this ami the two preceding sections be examined, by reference to Diagram 4, it will 
he observed that two elevations, crowned by St. Paul’s Rocks and Fernando Noronha 
rcsjtectivcly, divide the Atlantic at this [>art into three basins or depressions. 
OJf Bahia . — During the stay at Bahia the pinnace was engaged several days dredging 
in the bay. In some places the deposit was a white quartz sand containing fragments of 
felspar, mica, magnetite, hornblende, and other minerals, and also fragments of Echino- 
«lcrms, Polyzoa, Scrpula, and other organisms. In other places it was a dark blue mud. 
