Lansing Pleistocene Geology. — JVUicJiell. 265 
be set aside as mere academician's play, but with full accept- 
ance of the principle quoted above ; for with the non-applica- 
bility of that academic discussion there can be no application 
of the recent agencies — closest at hand in time — to which it 
refers. 
Essential Points of Professor Chamberlin's Discussion. 
In the course of the discussion of the special case professor 
Chamberlin makes the following points : 
1. "The upland surface is mantled with loess and loam, 
the main portion of which is probably referable to the lowan 
stage." 
2. The tributary valley is well adjusted in its debouchure 
upon the bottoms of the Missouri valley. 
3. The Missouri river rock-bluffs at the point where the 
tributary valley joins the Missouri "have been abruptly trun- 
cated by the waters of the Missouri," recently, i.e. since the 
Wisconsin stage, meaning thereby that the lateral erosive m^ 
tion of the Missouri has not only uncovered the preglacial rock 
bluff but has eaten further into it. 
4. "The tributary valley is not occupied by a constant 
stream, but by periodic run-off." The channel at present is in 
a slightl}^ aggraded and apparently still aggrading stage. 
5. The Missouri valley is in a degradational stage, i. e. 
the plane of its bottoms is being sunk deeper between the 
bounding rock bluffs. 
6. The depth of the aggradation deposit at the mouth of 
the tributary "is not known to me, but it is probably not many 
feet." 
7. The lower three or four feet of the materials pierced bv 
the tunnel "is composed mainly of limestone fragments and 
earthy debris, a part of the latter seeming to come from the 
Carboniferous becis, a part from the glacial drift or loess, and a 
part from the river and valley ^ash, in short a rather hetero- 
geneous mixture." 
8. "About three feet above the floor on the western side 
there is a definite layer of dark highly calcareous clay less 
than three inches in tnickness, but it does not appear on the 
opposite side." 
9. "Even in the inner end of the tunnel the silt [i. c. the 
upper part of the materials pierced by the tunnel. N. H. W.] 
