THE COBALT SERIES; ITS CHARACTER AND ORIGIN 141 
conclude that the evidence preponderates in favor of the hypothe- 
sis that the conglomerates of the Cobalt series were deposited 
from pre-Cambrian continental ice sheets. 
In the above pages an attempt has been made to apply the 
criteria which distinguish the various types of continental clastic 
sediments to the different rock types represented in the Cobalt 
series and thereby to reach a definite conclusion with regard to 
their origin. Asa result it has been shown that not only has every 
variation in the series its duplicate in the glacial, interglacial, or 
postglacial deposits laid down in association with the Pleistocene 
continental ice sheets of the same region, but that no other known 
depositional process will so well account for all the many peculiari- 
ties and associations of sediments found in the series as the glacial 
hypothesis. Furthermore, the objection that striated surfaces 
have not been found beneath the basal conglomerate loses much 
of its force when it is recalled that only an exceedingly small part 
of the contact between the Cobalt series and the older complex 
has been observed, that the underlying surface in some places 
has been smoothly eroded, and that the presence of the overlying 
conglomerate at those points generally makes an examination for 
striae impracticable. 
With the progress of detailed geological investigation in regions 
where pre-Cambrian rocks occur, evidence is accumulating which 
indicates that the processes at work on the earth’s surface today 
were in operation in the very earliest pre-Cambrian periods. The 
existence of pre-Cambrian continental ice sheets would therefore 
be simply another link in the chain of evidence pointing to the 
uniformity of natural processes from the very earliest time in the 
earth’s history of which we have any knowledge. 
