194 The American Geologist. September, 1894 
cized interpretations, is thai the submerged channels off the mouths of 
certain rivers are evidence thai such submerged channels are the re- 
sults of erosion, and therefore thai they marked periods of upheaval 
and depression of adjacenl lands. Whilst this may be true in some 
instances, ii by no means follows for all, nor for the deeper of these sub- 
merged channels.* < )hannel-building by bank elevation goes on as well 
under water as under air.f The sediments which these rivers have 
borne to the ocean during their entire existence (and particularly during 
the "Diluvial" and "Terrace" epochs) must have been deposited more 
upon llic flanks of the outflowing fresh water than in the direct lines of 
swiftest flow. If anyone will take the pains to plat to natural scale the 
sections of many of thesedeeply submerged channels, he will find that 
the slopes of the banks are not upon lines of erosion, but that they cor- 
respond more nearly to lines of sedimentation. Besides, before a sub- 
merged channel shall be decided to be one of erosion, not only should 
the form of the channel correspond to proper lines, but the material of 
its banks should be determined, and the eroded materials should be ac- 
counted for either in the extension of the bank lines or in the construc- 
tion of a bar at the eroded mouth. Therefore, the existence of a sub- 
merged channel is not always a proper and conclusive proof that the 
channel was formed by erosion and hence is evidence of ureal upheaval 
and depression of adjacent lands. Mar.SDEN MansON. 
San Francisco, Cal., July .'4th. 1894. 
Lake Cayuga a Rock Basin. Replying to Dr. Spencer's comments 
on my paper which states the evidence at hand pointing toward the 
conclusion that lake Cayuga is a rock basin. I would say that my fail- 
ure to include the continental tilting of the land was due to the fact 
that it would not essentially modify the argument, ami that I have not 
considered t he conclusions reached as definite enough to be accepted. 
Some tilting has taken place, hut much needs to be done before we can 
determine its amount in central New York. The problem is complex 
and requires a knowledge of the preglacial and the glacial attitude of 
the land, as well as the postglacial changes. 
1 do not deny that rock exists at a considerable depth near the outlet 
of lake Cayuga; indeed, 1 should be surprised if this were not the case. 
I cannot, however, agree with Dr. Spencer that this would force me 
from the use of the term rock basin to valley erosion. Valley erosion 
by ice means rock basin formation. The ice erodes, according to my 
argument, in broad north and south valleys; and when one of these val- 
leys l urns to the east or the west, or when it joins an east and west main 
stream, the marked it rosion ceases. If. for instance. Cayuga river 
flowed northward and was tributary to an east and west Canadian 
stream, the ice erosion deepened the vallev of Cayuga hut failed to 
deepen the east-west valley to a ureal degree; so that the north and south 
♦The following argument has been communicated to the editor of The Glacialists'' 
Magazine in a recent contribution by the writer. 
; r~. < Report "I Chief of Engineers, U. S. Army. iSS2, pp. 2=.?i . 1-22. Appendix MM; or 
1 \ Doc. No. 93, 411th Congress, 3d Session, pp. 7. B. 
