1906-7.] 
The Composition of the Red Clay. 
167 
XVII. — The Composition of the Red Clay. By F. W. Clarke, D.Sc., 
LL.D., Chief Chemist, U.S. Geological Survey. Communicated by 
Sir John Murray, K.C.B., F.R.S., etc. 
(MS. received April 3, 1907. Read May 20, 1907.) 
In the volume upon Deep-Sea Deposits, issued as one of the reports of 
the Challenger Expedition, there are published twenty-five analyses of the 
“red clay.” * This sediment is now recognised as the most extensive and 
important of all the oceanic deposits, for it covers 51,500,000 square miles 
of the sea-floor, and is characteristic of the greatest depths. It is therefore 
obviously desirable to know its average composition as exactly as possible, 
and for that reason the following investigation was undertaken. 
Of the analyses above mentioned, twenty-one were by Brazier, two by 
Hornung, one by Klement, and one by Renard. They are, however, not 
strictly comparable, as a glance at the recorded data will show ; nor are they, 
from the point of view of the modern analyst, so complete as they should 
be. For example, that ubiquitous element, titanium, was not determined 
in any of the analyses, for at the time they were made its importance and 
relative abundance were not appreciated. Other substances which are 
common in clays were neglected for similar reasons ; but their significance is 
now better understood, and improvements in analytical methods have made 
it easier to search for them. In Brazier’s analyses the alkalies were not 
estimated, but were reported by the other analysts — an omission in the 
first group that was not due to oversight, but to the limitations of the 
purposes for which the work was done. The general nature of the red clay 
was well established, its great variability in composition was clearly shown, 
and its relations to other clays were made sufficiently plain to satisfy all 
ordinary requirements. 
Of late years, however, it has become a matter of interest to determine 
the relative abundance and distribution of the chemical elements ; and in 
an inquiry of that sort so notable a substance as the red clay could not 
well be neglected. A new and more elaborate analysis of it, therefore, 
seemed to be required, and to that end two methods of investigation were 
available. First, it was possible to make a number of individual analyses 
* Deep-Sea Deposits , pp. 198, 201, and 425-435. 
