1909-10.] Composition and Character of Oceanic Red Clay. 183 
VII. — The Composition and Character of Oceanic Red Clay. By 
W. A. Caspari, B.Sc., Ph.D., F.I.C., Assistant at the Challenger 
Office. Communicated by Sir John Murray, K.C.B., F.R.S. 
(MS. received November 25, 1909. Read July 12, 1909.) 
The chemistry of this not the least interesting of deep-sea deposits, though 
it has received attention from several investigators in the past, still presents 
some uncertainties as regards both the analytical composition of the material 
and its chemical nature. It has therefore been suggested by Sir John Murray, 
to whom directly or indirectly all our knowledge of Red Clay is due, that 
the subject might with advantage be reopened from the chemical standpoint. 
The results of this revision, which was carried out in the Challenger 
Laboratory at Edinburgh, are set forth and discussed in the ensuing pages. 
Red Clay deposits were first met with by the naturalists of H.M.S. 
Challenger in 1873, some hundred miles west of the Morocco coast, and 
were so called from their resemblance, in consistency, to terrestrial clay. 
Regarded at first as a biological precipitate,* Red Clay was shown by 
Murray f to be produced mainly by the decomposition in the sea itself of the 
volcanic minerals, especially pumices, with which the deepest parts of the 
ocean are strewji. The general distribution of Red Clay, as mapped in the 
Challenger Reports, l was but little modified by the more recent soundings 
of the Valdivia, § Gauss, \\ and Albatross. 1[ Usually Red Clay borders upon 
and gradually merges into Globigerina Ooze deposits; there are consequently 
intermediate types of deposit which cannot be classified, except on an 
arbitrary system, as one or the other. Typical Red Clays should not contain 
above 20 per cent, of calcium carbonate, and those from 3000 fathoms or 
deeper contain very little, or none at all. 
All over the ocean Red Clay may be expected wherever the depth exceeds 
2000 fathoms. The total area occupied by it is about 51 million square 
miles ; in the Pacific it is the deposit par excellence, whereas in the Atlantic 
and Indian Oceans it occurs rather as patches in the Globigerina Ooze. 
* Wyville Thomson, Proc. Roy. Soc. Edin., xxiii. p. 47, 1874. 
t Proc. Roy. Soc. Edin., ix. p. 247, 1877. 
X In which the contemporary or shortly subsequent soundings of several other vessels 
are also made use of. 
§ Murray and Philippi, Wiss. Erg. Deutsch. Tiefsee-Exp., x. p. 4, Jena, 1908. 
|| Philippi, Verh. XV Eeutsch. Geographentages, Danzig, 1905, pp. 28-33. 
IT Murray and Lee, Mem. Mus. Comp. Zool., xxxviii., 1909. 
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