Wright.] 
142 
[January 19 r 
Doubtless the region north of Trenton shared in this depres- 
sion, but, being above tide-water, the effects would not be equally 
evident. The valley above Trenton is narrow. At Lambertville 
about twelve miles up the stream, a trap dike contracts the valley 
to a width of not more than one quarter of a mile. Above this 
point the supposition of floods sufficient to deposit the boulder- 
bearing clay is, perhaps, not incredible. For though the descent 
in the stream is now about four feet to the mile from the Dela- 
ware Water Gap down to tide level (about eighty miles), it was 
probably less during the Champlain epoch. For the depression 
of that period proceeded at increased rate northward. In 
Montreal it was five hundred feet ; in V ermont, three hundred 
feet; and how much more or less in the vicinity of Lake Erie 
we cannot tell, though the phenomena of the lake ridges would 
indicate that it was considerable, perhaps three hundred or four 
hundred feet. A depression gradually increasing north-westward 
would greatly diminish the velocity of the torrent of the Cham- 
plain epoch and the narrow places in the valley would greatly 
retard it. Professor Dana has shown that in the lower part 
of the valley of the Connecticut River the floods rose during the 
Champlain epoch from one hundred and fifty to two hundred 
feet above the present high water mark. The Connecticut River 
valley below Middletown is contracted by trap dikes much as the 
Delaware is at Lambertville. But the drainage basin of the 
Connecticut is three times as extensive as that of the Delaware 
(being twenty thousand square miles). This, however, is partly 
offset by the branch currents which, as Professor Dana shows, set 
off from the Connecticut at various places above Middletown. 
At any rate in the Delaware valley we find boulder-bearing 
clay rising to a height of one hundred and fifty feet above the 
present high water level. In the Lehigh valley, at Bethlehem, a 
few miles above its junction with the Delaware, and several miles 
south of the limit of the ice field, Professor Lewis and I found this 
boulder-bearing clay containing scratched pebbles and lying 
unconformably upon thick deposits of coarse stratified gravel at 
a height of one hundred and eighty feet above the river. Farther 
up the Lehigh valley also, near Weissport, we ascertained the 
limit of ice-carried boulders to be one hundred and eighty feet 
above the river. 
