1881 .] 
143 
[Wright. 
We are probably safe in assuming that these floods, depositing 
clay and boulders at the height above mentioned, mark both the 
period of greatest depression during the Champlain epoch and 
the period when the ice was most rapidly melting away. Of 
course the deposition of what Professor Lewis styles “ red gravel ” 
and the high gravels at Bethlehem occurred earlier, since the clay 
overlies them. These gravels I should assign to the early stages 
of the Champlain epoch. 
It is evident that the deposition, both of this red gravel and 
the boulder-bearing clay is separated from that of the implement- 
bearing gravel at Trenton by a period of vast physical changes, 
if not of vast time. 
Considering, now, this Trenton gravel, we find it to be 
limited at the head of tide water to a level of about forty feet, 
and diminishing in height relatively to the river both as one 
ascends and as one descends the channel, until at Yardleyville, a 
few miles above Trenton, it merges into the terrace which main- 
tains a pretty uniform height of fifteen or twenty feet above the 
river all the way to the Water Gap. Above the Water Gap the 
gravel terraces rise to a much greater height. At Stroudsburgh 
a second terrace stands seventy-five feet above the first terrace 
which is about fifteen feet above Broadhead Creek. But this 
upper terrace is kame-like in its structure, and hence would be 
explained in part by the lingering presence of the glacier itself. 
The descent of the river valley from Belvidere, where the ice 
sheet terminated, to Trenton is two hundred and thirty-two feet, 
or at the rate of nearly four feet per mile, as the river runs. 
The transportation of gravel by a river is dependent both upon 
the amount of material accessible to the running stream and upon 
the rapidity of the current. Toward the close of the glacial 
period the pebbles accessible to the stream were superabundant, 
having been deposited in excessive amount by the melting of the 
glacier in the lower latitudes. The water-worn pebbles at Tren- 
ton were probably largely derived from this source. Even a 
glacial torrent may have more loose material than it can manage, 
and so may silt up its bed with gravel. Hence it is not necessary 
to suppose the river at this point to have been of sufficient 
volume to fill the whole valley with water to the height of the 
