82 
Wisconsin Academy of Sciences , Arts and Letters. 
SOME ADDITIONAL EVIDENCES BEARING ON THE 
INTERVAL BETWEEN THE GLACIAL EPOCHS. 
By PRESIDENT T. C. CHAMBERLIN.* 
'Evidences bearing upon the interval between the glacial epochs may be 
drawn from various parts of the glaciated field and from the various 
phenomena connected with glaciation. It is not, however, my purpose to 
make any approach to an exhaustive review of these evidences, or even to 
touch upon the arguments that may be drawn from all the several sources. 
I desire simply to bring to your attention certain specific evidences that 
have an important bearing upon the length of the main interglacial inter¬ 
val and that lend themselves more readily to intellectual estimation than 
others. The evidences that are especially additional to previous knowl¬ 
edge are drawn from the lower Mississippi Valley, but, in connection w r ith 
these, I shall briefly refer to evidences drawn from other valleys that fall 
into marked harmony with these. 
In the lower Mississippi Valley, the sub-stratum consists of Tertiary de¬ 
posits. Upon these there is a thin stratum of gravel and sand, known 
heretofore quite widely as the Orange Sands, although that term seems to 
have been applied to different formations. This stratum has been very 
considerably misunderstood. It does not contain, so far as critical investi¬ 
gation shows, any material that may be regarded as glacial, although I 
think in some of the earlier reports Archean pebbles were cited as an indi¬ 
cation that these gravels were contemporaneous with the glacial deposits 
of the north. They have been critically examined during the summer by 
my colleague, Professor Salisbury, and during the entire season’s search he 
has not found a single pebble that is referable to a glacial origin. Some 
years since I examined the same formation with like result. Professor 
Call has also examined some of these deposits with a similar result. The 
pebbles are chiefly of chert and were derived from the chert-bearing lime¬ 
stones, largely Carboniferous, but reaching as far down as the Lower Mag¬ 
nesian limestone. They are, therefore, non-glacial. This is a matter of 
some importance as these sands and gravels have been correlated with the 
glacial deposits not only but referred to the Champlain epoch. They are 
very far removed from the Champlain deposits in time. That correlation 
is one of the great errors of Quaternary geology. They are certainly pre- 
* The facts relative to the Lower Mississippi region are drawn largely from the observa¬ 
tions of my associate, Prof. R. D. Salisbury. 
