194 
THE VOYAGE OF H.M.S. CHALLENGER. 
far from land. Even in the greatest depths, however, the remains of arenaceous 
Foraminifera and Annelids are to be found, while fishes and representatives of nearly 
;dl the invertebrate groups, such as Hexactinellida, Monaxonida, Asteroidea, Echinoidea, 
Criuoidca, Actiniaria, Polyzoa, Ophiuroidea, Holothurioidea, Tunicata, and Lamelli- 
branchiata, have been dredged and trawled from the red clay areas. The fragments 
of all the hard parts of these organisms may be met with sparingly in specimens of Ked 
Clay, but not in nearly such abundance as might be expected. 
When there are no remains of calcareous organisms in a Red Clay, or when in the 
laboratory these have been removed by dilute hydrochloric acid, the deposit or resulting 
residue is found to contain, in addition to the hydrated silicate of alumina and the 
remains of siliceous organisms above referred to, a large number of inorganic elements 
of a varied nature, derived from widely difierent sources. In the above-mentioned 70 
samples, the average percentage of residue is 93 ‘30. The most constant and widely dis- 
tributed of these extraneous materials are fragments of pumice belonging to the acid, 
neutral, and basic types of volcanic rocks. Rounded and angular fragments of these 
were dredged and trawled in great numbers from all depths, and in nearly all regions 
of the ocean, varying in size from masses larger than a man’s head down to the minutest 
particles. These were met with in all states of disintegration, some having undergone 
little decomposition, while others were surrounded by zones of alteration, or were so 
decomposed that the structure of the areolar pumice could with difficulty be recognised ; 
this was especially the case when the fragments were surrounded with a coating of 
peroxide of manganese or formed the nuclei of manganese nodules.^ All the mineral 
species usually found in the different varieties of pumice are accordingly present in the 
Red Clay, such as sanidine, plagioclase, augite, hornblende, magnetite, &c., and these, 
together with the glassy splinters and fragments of the pumice, are universally present 
and chiiracteristic of these deposits. Palagonite, which arises from the decomposition 
of the basic volcanic glasses, is likewise universally distributed, and in some regions of 
great extent there are numerous fragments of basaltic glass, basalt, and augite-andesite.* 
The peroxides of iron and manganese are found throughout the Red Clays in the form 
of minute grains or coatings, sometimes one of these oxides and sometimes the other 
predominating, each giving its characteristic tint to the deposit. When these oxides 
arc deposited as concretions ai’ound organic remains and other nuclei, they form the 
now familiar manganese nodules, especially abundant in those red clay deposits 
where the debris of basic volcanic rocks arc present }ind have undergone great alteration.® 
Minute black magnetic s{)herules, often with a metallic nucleus, which are regarded as 
having, together with other particles, a cosmic origin, are probably everywhere j^resent 
• Murray, /'ror. Koy. Sor. Eriin., vol. ix. pp. 249-252, 1877. 
« .See Pi’. XVI. fig*. 1-.3; PI. XVII. fig8. 1, 2; PI. XVIII. figs. 1-4; PI. XIX. figs. 1, 2, 4; PI. XXI. figs. 1, 2. 
» Sec PI. XXVIII. figs. 1-6; PI. XXIX. figs. 1-4. 
