396 
THE VOYAGE OF H.M.S. CHALLENGER. 
of the contiueutal shelf, the deposit in each case being a Green Sand, in depths of 
98 and 150 fathoms, while the third station is situated in the deep water to the 
south of the Bank, in 1900 fathoms, the deposit being a Globigerina Ooze. 
The mineral ogical elements of the Green Sand (Stations 141 and 142) may be 
considered as derived from the neighbouring land, consisting of quartz, garnet, green 
hornblende, black mica, kc., and the coast character of the deposit is still further 
indicated by the large quantity of mineral particles left in the residue after treatment 
with acid, and also by the presence in abundance of typical grains of glauconite, 
a mineral never found, we may say, in truly pelagic deposits. The analogy 
between this sediment and the greensands of geological formations cannot be mis- 
construed, and the conditions under which they have both been formed must be 
nearly identical. As the distance from land and the depth of the sea increase, the deposit 
assumes a more pelagic character, and consequently at Station 143 the mineral particles 
are for the most part those found in the open ocean, being mostly of volcanic origin ; 
this Globigerina Ooze, however, being formed at a point not very far removed from 
land, is not purely pelagic and still contains particles of quartz, indicating with 
considerable certainty the proximity of land. This deposit may be compared with 
the white chalk of geological formations, but in this case the Ehizopod shells, 
constituting the mass of the sediment, are preserved entire, and belong to pelagic 
species, while in the chalk the Foraminifera are chiefly bottom-living forms, and have 
generally been broken or reduced to powder by agencies posterior to sedimentation. 
During the Challenger Expedition, phosphate of lime was procured at many of the 
shallower stations around continental shores, but never in such abundance or such 
typical development as at these stations to the south of the Cape of Good Hope.^ 
j\Ir Murray has described similar phosphatic concretions from the dredgings of the 
U.S.S. “Blake,” along the Atlantic coasts of North America.^ In one instance the 
nucleus of the concretion consisted of a fragment of a manatee bone, but in the majority 
of cases the nodules consisted of an aggregation of calcareous organisms cemented by a 
brownish yellow phosj)hatic matter, often showing concentric rings, after the manner of 
agates, thus indicating deposition from solution. 
It may be pointed out that phosphatic nodules are apparently more abundant in 
the deposits along coasts where there are great and rapid changes of temperature, 
arising from the meeting of cold and warm currents, as, for instance, off the Cape of 
Good Hope and off the eastern coast of North America. It seems highly probable that 
in these phices large numljers of pelagic organisms are frequently killed by these changes 
* In the material (lredg(fd by the German ship “ Gazelle” on the Agulhas Bank, which Mr Murray was permitted 
to examine at Berlin, there were numerous phosphatic ami glauconitic nodules identical with those procured by the 
Challenger. 
* JJuU. Mu*. Comp. Zoijl., vol. xii. pp. 42, 43, 52, 53, 1885. 
