186 
IOWA ACADEMY OF SCIENCES 
The rational interpretation seems to be that Nos. 5 and 4 were de- 
posited in an old bend of the river when its surface was about 40 feet 
higher than at present, the sand being the true river deposit, while the 
loam and dark mud record the accumulation after the bend had become 
a bayou. The slope which overlaps it and gives an impression of a sec- 
ond till is probably the caving and wash from the cut bank back. It is 
interesting to note that this bend would correspond to the Unio Terrace 
which Dr. Bain noted at several points, and considered pre Wisconsin. I 
can see no sufficient reason, however, for considering it very ancient. 
4. Professor Wilder in his Geology of Lyon and Sioux counties, 
thinks he has found reason to locate the Altamont moraine east of Sioux 
Falls and of the Big Sioux further north, instead of south and west in 
a broad curve, west of Wall Lake as was done by the writer. There is 
not time now for discussion, but the writer wishes to reaffirm his for- 
mer interpretation of the tacts, with much confidence so far as concerns 
most of the moraine. Possibly a comparatively faint and early member 
may be traced along the line he indicates. 
In this connection the writer would add that after a re-examination 
of the cuts along the Illinois Central and Sioux Falls, which were visited 
jointly by Bain, Leverett and himself, and treated by him in Proceedings 
of I. A. S. Vol. VI, p. 125, he returns to his former interpretation, viz: 
that they are all in an old terrace of the river. The terrace topography 
and the general character of the deposits are his main reasons, which 
time prevents giving here in detail. 
5. Time permits the very brief discussion of only one more “vari- 
ant”. Prof. McBride, in his discussion on Clay and O’Brien counties 
(Iowa Geol. Survey, Vol. XI, p. 488), records 700 feet to water in a 
well east of Primghar and another 1,000 in Caledonia township, and 
apparently infers that the till probably goes to those depths. That is 
certainly deep enough to reach the Dakota, and it seems more rational 
to believe that 5-600 feet of that depth is Cretaceous. Similar records 
are frequently given in South Dakota, where it is clear that such is the 
case. In fact if no sand is found or noticed separating the till from the 
Cretaceous few can tell when the drill passes the line of separation. 
The concretions in the shale simulate closely in shape, hardness and fre- 
quency the boulders and pebbles in the till. And the till often has almost 
the same composition as the shale from which it has been mainly formed. 
With this the writer v/ould respectfully submit this paper to your 
candid consideration and kindly judgment, and only hopes that it may 
be of some service, if not to others, to himself, through criticism by 
others. 
