from the melting of the Quaternary Glacier. 95 
sediment principally upon one side, making the highest normal 
terrace quite ditferent in elevation 
To understand this explanation, Mr. Upham’s idea as to the 
filling of the. valley with deposits before the making of the 
channel-way, considered on the preceding page, must be in 
mind. If the making of the channel-way and terraces went on 
together, as appears to have been the case, some other conclu- 
sion, both as to the “delta-terraces” and the ‘ highest normal 
terraces,” must be found. The terraces of the latter kind, in 
loaded ; a pitch of /en feet a mile under the last-mentioned con- 
dition would be large, of fifteen, very large, and of twenty feet, 
improbable. Only in case a tributary had ridges about its 
Mouth so as to favor the formation of a dam, or had had its way 
