222 The American Geologist. ^p"*' i^oi. 
ley as are needed to account for the deposition of the Tuscum- 
bia boulders, and for most of the complicated facts connected 
with the loess of the region. 
As the loess does not extend up the Osage valley as far as 
Tuscumbia, this may be urged as an objection to the theory 
here maintained. But a little reflection will show that it is not 
a fatal objection. The current of water setting up such a side 
tributary would necessarily be limited each season to a single 
filling of the channel with silt-laden water, while most of the 
silt would be deposited near the mouth where it eniered. Very 
little silt would remain in suspension when the slow-moving 
current had reached so distant a point in the cul de sac. 
An additional irresistible inference from the facts is that 
not only were the Tuscumbia boulders floated into their place 
during the later stages of the Glacial period, but that this oc- 
curred not a great many thousand years ago, and so furnishes 
an additional argument in support of other calculations which 
bring the closing stages of the Glacial period down to within 
the limits of about 8,000 or 10,000 years ; for, as has already 
been said, the large granite boulder on Mr. Barron's farm lies 
upon the top of a sedimentary terrace barely 20 feet above the 
present high-water mark of the river, and about one-third of 
the way, or 300 feet, between the present bank of the river and 
the rocky bluff upon the west side. This sedimentary terrace 
is now in process of degradation. The river is striking against 
it, now upon this and now upon that side of the valley. The 
small amount of work already accomplished in its degradation 
is clear proof that it has not been at work for an indefinite 
period of time, but at the outside for only some such period as 
is indicated by the shorter chronological calculation for the 
close of the Glacial period. 
