i8 9 i.j 
331 
[Davis. 
material washed into the trench of the Catskill between its 
evacuation by the ice and the elevation of the land was at least 
one tenth of a cubic mile — a surprisingly large measure. The 
terracing since the elevation of the region has excavated more 
than half of this amount, over a twentieth of a cubic mile of sand 
and gravel. To be sure, this excavation has been wrought in 
unconsolidated materials, but it is of surprising quantity in any 
case ; and when it is remembered that this double work of filling 
and cutting away has been done in the brief time since the ice 
retreated, during which our kames and eskers and drumlins have 
lost so little of their constructional forms, the contrast between 
the rates of surface-wasting and of stream-carrying is clearly 
brought out. There is another impressive contrast to be seen 
between the stability of the solid rocky walls of the valley and 
the rapid growth and wasting of the loose valley-filling. The 
valley walls have not changed materially since the ice left them ; 
indeed, they are not now much different from their preglacial 
form. During the excavation of such a rock-walled valley, there 
might be many episodes of filling and washing out again, such 
as that now illustrated by the terraced post-glacial sands and 
gravels. 
The most notable feature in the excavation or terracing of the 
valley-filling is the great variation in the width of the present 
flood-plain ; and in this, one may see good reason for accepting 
the conclusion stated above, that the whole valley was at the end 
of the period of depression filled with sands and clays from 
side to side as high as the present terrace benches. When ter- 
races on either side of a valley stand at about equal distance 
apart, the question is sometimes raised whether the intervening 
space was ever entirely or even for the greater part filled with 
the terrace deposits ; but in the case of the Catskill, such a ques- 
tion would hardly arise. 
The farmer who told us of the deep sands in the Potuck delta 
mentioned a fact of interest concerning the broad flood-plain 
meadows of the Catskill : the fine soil of the meadow is under- 
lain at a depth of five or more feet with coarse water-worn 
cobbles, such as now occupy the channel of the Catskill. From 
this, it may be fairly inferred that at one time or another, since 
the acceptance of the present local baselevel as determined by 
the falls at Leeds (see below), the stream has swung from side 
