The Missouri Lead antl Zinc Deposits. — Rohevtson. 245 
ooiitents and as to whether the metals found in rocks were not 
introduced subsequently to the deposits of ore. In regard to 
the first point, it is not at all necessary to confine the area of 
supply to the immediately adjacent rocks ; and in regard to 
the latter point, while it would be impossible to prove its 
falsit}^ it is in many cases highly probable that the minerals 
existed diffused in the rocks, from the fact that they are found 
in similar rocks in areas removed from ore deposits. 
The applications of this theory, heretofore, however, appear 
to be inadequate to explain these deposits. Prof. Chamberlin's 
explanation of the Wisconsin deposits and, incidentally, of those 
<^)f iMissouri, introduced lateral secretion as a secondary cause, 
the primary one being concentration b}' oceanic currents in 
the Lower Silurian seas. This does not cover the case of the 
large Lower Carboniferous deposits of Missouri, and appears 
to be too theoretical to satisfy the demands of the case. Mr. 
F. C. Clere suggests that the deposits were derived by lateral 
secretion from the Coal Measure shales. For this he requires 
a Quaternary submergence during which these shales were 
leached and their metalliferous burden dejjosited in the Lower 
Carboniferous rocks below. These Coal Measure shales, how- 
ever, are very impervious to water and are not associated with 
all of the deposits, by any means. Moreover, no deposits of 
any importance are found in Coal Measure rocks, as would be 
expected. 
The hypothesis here advanced to account for the origin of 
these metalliferous solutions is that of concentration through 
surface decomposition. This h3q)othesis starts with the prop- 
osition that the metals existed originally in the Archean 
crystalline rocks either diff'used or in veins. On the degratla- 
tion and decomposition of these rocks, the metalliferous min- 
erals were parti}' transferred to the Silurian rocks and from 
these in a like manner transferred to the rocks of the Lower 
Carboniferous stage. Here the surface decomposition, ex- 
tending through long periods, favored local concentration of 
the minerals in the meteoric waters and these, penetrating 
downward, deposited their load whei'c contlitions were favor- 
able. The widespread occurrence of lead and zinc in nature 
is treated of in a comprehensive wa}' in the report referred to.* 
*Mo. (ieol. Surv. Report on Ijcad aiul Zinc, Pt. 1, p. :50. 
