362 Story of the Mississippi-Missouri .— Clay pole. 
our day the dim outlines of what then existed. We are be¬ 
ginning to suspect the action of causes of which we see few 
traces in recent times, the occurrence of changes on a scale 
and of a nature that can no longer be matched, and the lapse 
of aeons whose length must be measured with a different unit 
from any of those in use for later eras. The Archaean age in 
fact is a simple expression for a complex reality which we 
have not yet begun to comprehend, a single word to denote 
almost an eternity. For even when we have made all pos¬ 
sible allowance for greater intensity of causation and there¬ 
fore for vaster results in equal times the conviction grows 
with investigation that the Archaean age was far the longest 
of the four and perhaps as long as all the other three together. 
The view of that distant field, even with the aid of the 
powerful telescope of geology and with the strong light which 
is now thrown on it is however so dim that for the purposes 
of the present review it will be disregarded and no further 
reference will be made to it. Our sketch will begin at or about 
the commencement of the next or palaeozoic age. 
In attempting to bring into one view what is thus far known 
or has been rendered highly probable concerning the geologi¬ 
cal history of the Mississippi-Missouri river-system the writer 
claims no merit for originality. His aim is solely to unite 
into a whole what is well known to every American geologist 
whose attention has been turned to this department of his 
favorite science. It is moreover quite possible that in some 
of the details there may not be perfect agreement. This is, 
however, a matter of secondary moment and if further con¬ 
sideration and discussion should modify the story in particu¬ 
lar parts and reduce it into closer accord with nature one 
purpose of the writer will be served. 
The commencement of the palaeozoic era shows us the ear¬ 
liest condition of North America that is at present attainable. 
It was then lying for the most part below the waters of an 
immense ocean. Where now we see the busy midland, eastern 
and southern states, rolled its waters tenanted by strange 
forms of life long since extinct. Since that ocean existed 
millions of years have elapsed and save for the researches of 
geologists its very existence would never have been known. 
Variations doubtless occurred from time to time in the outline 
