2.y2 The American Geologist. ^^J'- i^*^^- 
are composed of northern gravel derived from the Wisconsin 
glaciers, hut toward the south are formed of whatever mater- 
ials the surrounding countr}- could supply, and that they de- 
scend southward faster than the present descent of the rivers 
that formed them, so as to disappear by submergence under 
the wider bottom lands, are propositions that are admitted by 
most Pleistocene geologists. That the Missouri has, in some 
places, excavated a channel into the deposits of the Wiscon- 
sin epoch, forming Wisconsin terraces, and at others has filled 
its pre-Wisconsin channel by additions to its flood plain, is 
quite certain. That this excavation should be toward the 
north and this re-filling toward the south is also quite certain. 
Whether the Concannon farm is above or below the point of 
transition from the latest re-excavation to the latest refilling, 
it is impossible, from any data at hand, for the writer to state. 
It seems to be below% and therefore that the present resultant 
of scour-and-fill at that point is a small addition to the hight 
of the flcodplain. But owing to the importance attached to 
this by the hypothesis urged by professor Chamberlin the 
reader will find a more ample discussion of it under No. 22. 
6. The shallowness of the aggradation deposit at tlie 
mouth of the tributary is very important to the hypothesis of 
professor Chamberlin. If it is deep enough to show ex- 
cavation in the rock in the manner of a gorge it implies that 
the creek occupies an inherited channel, ard that the Mis- 
souri also must have been running at a lower level when that 
gorge was excavated, and no such event has taken place since 
the Wisconsin ice-epoch. The statement of Mr. Michael Con- 
cannon that a well sunk twenty-foiir feet in the creek bottoms 
a little east of the mouth of the tunnel did not encounter bed 
rock and that piling thirty feet long was driven for the support 
oi the bridge, is all the information the writer has bearing on 
this point directly. But inferentially he has much evidence that 
the creek had a pre-glacial adjustment with the pre-glacial 
Missouri at a considerable depth below its present adjustment 
plain. In the first place, the whole surrounding topographic 
contour shows that this creek's valley is exactly like almost 
innumerable tributary valleys that enter the Missouri and the 
Mississippi rivers south of the Wisconsin morainal belt. There 
is no topographic, nor other, reason to exempt it from the 
