on board H.M.S. 'Challenger. 3 527 



deposit, composed principally of the frustules of Diatoms and their 

 broken-down parts. In addition, they contained a good many Eadiolarian 

 remains, a few specimens of one small species of Globigerina, a few par- 

 ticles of mica, quartz, and granitic pebbles, also a little amorphous blue 

 clayey matter. No manganese particles were noticed. The one of these 

 soundings which is nearest to the ice contains much amorphous clayey 

 matter and larger mineral particles than the other two. When dried 

 this deposit is of a white colour, and is very light. 



The following are the depths of the soundings referred to above : — 



fms. fms. fms. 



1260 1975 1950 



5. Bed and Grey Clays. — By far the most abundant oceanic deposits 

 are the deep-sea clays. These are of a grey, red, or dark chocolate-colour, 

 and are found at depths greater than 2000 fathoms. The red and choco- 

 late-colours of many of these clays is due to the presence of the oxide of 

 iron in the first and of oxide of manganese in the latter instance. Most 

 of them contain some carbonate of lime in the form of Globigerina-shells ; 

 in one or two instances, however, I have not been able to find a single 

 shell, nor has acid caused the least bubble of effervescence. The remains 

 of siliceous organisms occur also in great numbers in the clays of some 

 regions — so much so that, as I have stated, some of those soundings in 

 the Worth-west Pacific which have been classed as clays might have been 

 called Radiolarian ooze. In most places, however, they are nearly or 

 quite absent. These clays are not amorphous in the true sense of the 

 word — not amorphous in the sense in which a chemical precipitate is 

 amorphous. They all contain small white and other coloured mineral 

 particles in great abundance — exceedingly small particles, so as to be 

 recognized only under the high powers of the microscope. They contain 

 amorphous matter, it is true ; but it is doubtful if this ever makes up so 

 much as a half of any sample in bulk. They also contain larger mineral 

 particles, as quartz, mica, pumice, scoria, peroxide of manganese, and 

 other mineral particles. Quartz and mica particles appear to be present 

 only in some localities, as the North Atlantic and elsewhere. Peroxide of 

 manganese is perhaps always present in the form of grains or nodules, 

 sparingly distributed in some regions, in others making up nearly a half 

 of the deposit or formation. 



Pumice (the common felspathic or the highly vesicular augitic variety) and 

 scoria appear to be universally distributed over the bottom of the ocean, 

 and to be abundant in most of the deep-sea clays and present in them all. 

 In those clays furthest from continents and islands sharks' teeth, ear-bones 

 of whales, other bones of whales, and bones of turtles (?) are very fre- 

 quently found, all these having usually a more or less thick coating of 

 peroxide of manganese. The following are the depths at which we 

 have found these red and grey clays ; — 



vol. xxiv. 2 Q 



