124 J. D. Dana— Phenomena of the Champlain Period. 
within the boundaries of the same great channel as it passed 
into the greater channel of the bay; and that this broad Mill 
River channel of the Glacial era through the soft sandstone 
was deepened at that time, if not made, by the excavating 
action of the ice and running water. The phenomenon is one 
now known to have been a common result of the glacier flood, 
in which a stream had its Glacial-era channel partly obliterated 
by the depositions from the waters as the flood from the melt- 
ing made progress. The deposits appear to have early blocked 
the channel, even before half-flood was reached, and thus forced 
ill River to take its present course. It is probable thata 
diminished slope in the land aided the depositions in checking 
the stream. 
The origin of the great depressions is thus traced to exca- 
vating-work in the Glacial era and subsequent depositions of 
drift material. They are the unfilled portions of the old chan- 
nel, and were left unfilled, while deposition was going on s0 
freely, because of the depth of the excavation, or, for parts of 
them, because of the position with reference to the main cur- . 
rent. The waters of the rising flood made a new exit for each 
of them, the Beaver Pond depression having opened a western 
outlet to West River, and the Pine-Marsh depression taken 
its northern extremity for discharge into Mill River. The dis- 
charge of the Beaver Pond waters was of long continuance, 
and held on through the era of maximum flood; for the depos 
its of the terrace adjoining the exit channel are of very coarse 
gravel, while elsewhere about the depression they are of fine 
gravel or sand. : ; 
The mean width of the Pine Marsh and Beaver Pond depres- 
sions has been stated to be 1000 feet. But the actual width in 
some parts is 2000 to 3000 feet; and as these depressions are 
only what was left after the burial, the mean breadth was 
probably near the present extreme breadth, or at least half a 
mile; and this comports with the supposed size of the stream. 
~The connecting lines between the Beaver Pond depression and 
Kast Creek are half a mile apart, and they may be the outer 
portions of the one broad channel half a mile wide. Hast an 
est Creeks are only two-thirds of a mile apart; and these 
may have been the sides of the channel at its mouth, for the 
channel would not there have been narrower but rather wider 
os 
See 
rT ¢ : 
proves that they originated at the same time with the depres- 
