THE COBALT SERIES; ITS CHARACTER AND ORIGIN 133 
or temperate climates,’ but is not characteristic of warm humid 
climates.? Since this region, at the time the soil was formed, was 
practically a peneplain, the topographic factor may be eliminated. 
If it be assumed, therefore, that the variations in the conditions for 
soil development were the same in pre-Cambrian times as at present, 
the climate which preceded the deposition of the Cobalt series was 
either cold and humid, temperate and humid, or arid. 
It is possible that owing to the absence of abundant vegetation 
to supply carbon dioxide to the ground water, or because of differ- 
ences in the composition of the atmosphere, the relationship of the 
chemical decay in the soil to climate may have been somewhat 
different at that early period, but it is doubtful whether this would 
be of sufficient importance to modify the foregoing conclusion. 
The abundance of limestone in some of the early pre-Cambrian 
formations indicates that carbon dioxide was certainly present in 
the atmosphere at the very beginning of geological time and may 
have been more abundant than in later periods, for it seems prob- 
able that the loss of carbon dioxide from the atmosphere through 
the formation of limestone and coal beds, since the pre-Cambrian, 
has been greater than the additions from other sources. 
3. Lacustrine deposition—The uniformly stratified argillite, 
greywacke, arkose, and quartzite which form a considerable part 
of the Cobalt series were evidently deposited from standing bodies 
of water and are therefore flood-plain or lacustrine deposits. How- 
ever, from the general greenish-grey or green color of all these 
sediments, from the absence as far as has been observed of mud 
cracks, rain prints, or other evidence of exposure to the air,’ in 
even the fine grained argillite, and from the presence of uniformly 
continuous ripple marks in the quartzite, it seems safe to conclude 
that these deposits have not been laid down from either flooded 
rivers or ephemeral lakes, but were deposited from permanent 
bodies of water which persisted from year to year. 
*T.C. Russell, Bull. 52, U.S. Geol. Surv. (1888), p. 12; G. P. Merrill, Bull. Geol. 
Soc. Amer., VI (1895), 321-22. 
2E. W. Hilgard, Soil (1906), 398-417. 
3 J. Barrell, Jour. Geol., XVI (1906), 538; J. Walther, Einleitung in die Geologie 
(1897), p. 846. 
