l-?'2 7 he American Geohxjlsi. Fcbnuuv, isws 
M\. I'lof. Salisbury's paragraph concerning my position u[K)n tlie 
unity of tlic glacial epocli is ill considered and misleading. He says 
that I should have indicated tliat my view is that of the minority. I 
am at a loss to know how I could have expressed that idea more 
clearly than 1 have done on page 110. in introducing my formal discus- 
sion of the subject, where all T claim is that, notwithstanding the po- 
sition of Pres. Chamberlin and many others, the theory of the .unity 
of the glacial epoch "is capable of being maintained without for- 
feiting one's rights to the res|)ect of his fellow geologists." As to 
what is the actual InMulof sentiment, (liei-e is. however, much room 
for (lilference of ()|)inii)n. One need not l)e ashamed to be in company 
with such authorities nixm glacial subjects as Dana, Hitchcock, Up- 
ham, Falsan. l*restwicli. Kendall. I>ami)lugh,IIuglies, Iloltz, Credner, 
Diener, Nikitin, and nuinerous otliei-s. It is significant that Nikitin, 
at the head of the geological survey of Russia, has just i)ublished a 
long ])a]ier in which he maintains that the glacial (le|)osits of that 
region give no evidence of more than one epoch. 
4th. I'rof. Salisbury says that I maintain tliat oceauic waters 
'■|)robably" reached southern Illinois and Indiana. What 1 said was 
that "it is perhaps necessary to- suppose." If I'rof. Salisbury thinks 
that means probably, he is welcome to the opinion. 
■5th. I will say but a lew words concerning the (Mnciinuiti ice-dam. 
I have taken pains to give my readers the information that ui)on this 
l)oint there are differences of opinion, and that Prof. Chamberlin is 
opposed to my view. 
Whether Prof. Chamberlin's strictures upon this theory, in his intro- 
duction to my report upon the subject, in Bullet in 58 of the United 
States (ieological Survey. CDiilain the liiial word upon the subject 
may be a fair (|ueslioii of doubt. .Vt any I'ate. I have not been 
ashamed to have tlie two documents circulated together ; for, to men- 
tion only twi) |)oints in his introduction, we find Prof. C'hamberlin 
admitting that "tlie ice-sheet i)robably pushed across the river, and 
landed the bouldery drift south of it essentially in its present posi- 
tion." Now, the Canadian l)oulder. of which I give an illustration on 
page ()3, is three feet and a half in diameter upon a hight of land fully 
six miles south of the river at its nearest ])oint. How Prof. Chamber- 
lin could maintain, as he does, p. 18. that the i)onded water of the 
upper ohiii would |)robably lift '"bodily" the massof ice which carried 
these glacial deposits so far south of the river is more than I could 
ever understand, for the specific gravity of ice is such that seven or 
eight feet will remain under water when one is above. To have 
carried the glacial material into Kentucky as far as has been done by 
so thin a ]iiece of ice that 500 feet of water would float it, is well-nigh 
an absurdity. 
.\s to other ])ort ions of his introduction, it is sufficient to say that 
doubtless many things were at first attributed to this probable ice- 
dam which must be explained by other causes. But that Prof. Cham- 
l)erlin has exjilained '/// the facts away is by no means so clear. In 
