106 
THE VOYAGE OF H.M.S. CHALLENGER. 
the otlier hand, in some areas the unaltered splinters of pumice, the fragments of volcanic 
;ishes, and minerals from floating ice, may augment considerably in size and abundance 
and make up 20 per cent of the deposit. One of the great characteristics of the Red 
Clay, however, is that the mineral particles over 0'05 mm. in diameter are few in 
number, and these have generally undergone alteration. The extreme fineness of the 
mineral particles, indeed, permits the relatively small quantity of pure clay to give a much 
more }>lastic character to the deposits than if these particles were of large size. 
The mineral particles' in the Challenger samples of Red Clay make up on an average 
5’56 per cent, of the whole deposit; they are generally angular, being recorded as 
rounded and angular in eight cases and rounded only in one case, and have a mean 
diameter of 0'08 mm. They are mentioned as occurring in the following order of 
abundance; — magnetite (in 62 cases), manganese grains and fragments (55), felspar 
(53), glassy volcanic particles (45), augite (43), pumice (34), manganese nodules (32), 
pellets, j)ieces, and nodules of pumice (31^), hornblende (31), palagonite (22), quartz 
(21), plagioclase (20), mica (19), phillipsite or zeolitic matter (lO), cosmic spherules (8), 
•sanidine (7), scoriae (6), glauconite (6), olivine (5), lapilli (5), rock fragments (5), zircon 
(3), tourmaline (3), epidote (2), garnet (-1). 
The Challenger trawlings and dredgings obtained sharks’ teeth in 1 1 cases, and ear- 
bones and other bones of Cetaceans in 6 cases. 
It has been stated that in marine deposits the species of unaltered particles of minerals 
with a diameter of not more than 0*02 mm. can in many cases be determined (see p. 25), 
and the fragments of pumice even less than that can also be recognised, but the particles of 
this size are usually very intimately associated with the clay of the deposit, and generally 
pa.ss away in decantation with the imj^alpable matter, which we have denominated “ fine 
washings.” These fine washings consist essentially of the hydrated silicate of alumina, 
mixed with an immense number of recognisable and unrecognisable particles of minute 
dimensions, derived from all the other materials which combine to form the deposit, such 
as minerals. Diatoms, and Radiolarians. It is quite natural to conclude that the mineral 
particles, mixed wdth the clayey matter in the fine washings, are of the same nature as 
tho.se of larger size which can be identified, and that quartz, felspar, &c., may be present 
in a very fine state of division as ultramicroscopic bodies, but this cannot be made out 
witli the microscope, chemical analy.sis only gives an indication.^ 
' St-e I'l. XXVI. figs. 2-4 ; PI. XXVII. figg. 2, 3. * In five cases distinctly stated to be covered by manganese. 
* It if- known that clny has the power not only of absorbing and of redlining certain liquids, but that it even 
f>o<^3eswa a similar projarty in the case of certain solids of very small dimensions. If, for example, clay be agitated in 
water, microacojfic grains of carbonate of calcium and particles of an organic nature will remain in suspension as long 
as the wafer is ngitate«l, but as soon ns the water is at rest these are dejK)sit<-d. These jfarticles are thoroughly pene- 
trated by the water, ami form a colloid gelatinous mass ; the jiarticles are found to be in contact, and .so attached the 
one to the other that it is not jiossible by the agitation of the water to deUich them. This mutual attraction or 
inteqa-netmtion takes jiloee not only with imrticlcs of the same nature, with clay for examjfle, but in the case of clay 
with hydrated [MToxi«lc of ir<jn, clay with chalk, clay with organic particles, so that it is dillicult, if not imiwssible, to 
