788 F. W. CLARKE 
form, quite unlike its common granular variety, and therefore not 
so readily recognized. ‘This is a mere suspicion, not entitled to much 
weight at present, but worth considering in future investigations. 
My specific problem has been to study the distribution of the chemi- 
cal elements in nature, and to that end the composite analysis of the 
red clay is a step forward. 
U.S. GEOLOGICAL SURVEY 
WasHinctTon, D. C. 
March 14, 1907 
ADDENDUM 
Since the foregoing pages were written I have received from Sir 
John Murray a composite of 52 “terrigenous” clays, dredged up 
from oceanic depths ranging from 140 to 2,120 fathoms. In the 
nomenclature of the ‘‘Challenger” expedition, 48 of the individual 
samples are classified as “blue muds,” and 4 as “green muds.” 
Twenty-three of the clays were collected by the “Challenger;”’ the 
others were brought in from voyages of the “Buccaneer,” “ Dart,” 
“Egeria,’ and “Rambler.” ‘The range of collection, as in the case 
of the “red clay,” was world-wide, and all of the great oceans are 
represented in the composite sample. 
Molybdenum and zirconium were not detected. Nickel, cobalt, 
lead, zinc, and arsenic, which were reported in the red clay, were 
not looked for. Apart from these trivial omissions, the red and ter- 
rigenous clays are fairly comparable. The red clay is lower in silica 
and alumina, but higher in iron than the muds, and other minor 
differences appear. The high manganese of the red clay may be 
correlated with the abundance of manganese nodules in the greater 
oceanic depths. The results of analysis appear in the following 
table: 
A. General analysis by Mr. Steiger. 
B. Portion soluble in water. 
C. Analysis reduced to standard form by rejecting soluble salts, calcium car- 
bonate, and hygroscopic water, and recalculation of the remainder to 100 per 
cent. 
