294 The American Geologist. ^^'^'' '^^^^■ 
the geest hj'potliesis ? Would geest be likely to have so abrupt sur- 
face under it? I confess that I did not think of geest when I was 
there. I did not observe much contrast in color or texture from top 
to bottom except that there were more stony fragments below as one 
would expect from a waterlaid deposit near a slope of Carboniferous 
limestone and shale. 
From our former correspondence and conversation, you will not be 
surprised at my view. I have not attempted to answer all your strong 
arguments, but have tried rather to improve the opportunity you have 
so kindly given me in presenting briefly my humble contribution to 
the interesting questions involved. 
Yours very respectfully, 
Vermilion, S. D., March 7, 1903. J. E. Todd. 
Note from Professor Wright. 
Oberlin, Ohio. 
Prof. N. H. Winchell, 
Dear Sir : — I visited the Concannon farm and made my examina- 
tions soon after you were there the second time, but I did not have 
opportunity to make the minute observations which you are able to 
report. So far, however, as I was able to form conclusions, they agree 
essentially with those presented in your paper on "The Pleistocene 
Geology of the Concannon Farm." I followed down the main tributary 
valley all the way from its head, to its opening upon the Missouri 
valley close by the tunnel in question, and followed around the head 
of the smaller valley which joins the main tributary at right angles to 
it just west of the Concannon house. From these observations it 
' seemed perfectly clear that very little rock erosion had been accom- 
plished by these tributary streams' subsequent to the deposition of the 
general covering of upland loess. They have done scarcely more than 
to remove from the pre-Iowan, (or as I think the pre-Glacial) valleys 
the loose material which has been carried into them during Glacial 
times. 
This is specially clear, as you have pointed out, from the character 
and extent of the depression immediately in front of the tunnel and ex- 
tending from the point A in your figure to the edge of the Missouri 
flood-plain, but which is now filled with loose debris. The stratum 
of limestone surrounding this depression and forming the floor of the 
Concannon tunnel is compact and about six feet in thickness. The de- 
pression has every appearance of being formed by the recession of the 
waterfall where the limestone was underlaid by shale. From consider- 
able familiarity with the recession of waterfalls in similar conditions 
since the lowan epoch, it is impossible to believe that this small stream 
would not have required many times the period which has elapsed 
since then to accomplish its work. I can but regard it, therefore, as 
pre-Iowan, and for the most part pre-Glacial. 
2. There is no evidence that the water of the IMissouri has been 
higher than it is now since the flooded condition of the lowan epoch. 
