220 LW. S. Shaler—Fluviatile Swamps of New England. 
streams come, therefore, as a corroboration of an hypothesis 
which has perhaps sufficient verification from other evidence. 
The chief interest of the facts indicated by the valleys we have 
been discussing is that they give an approximate measure of 
the amount of dislocation of the continent on the southern part 
of New England, and that they apparently show that the down- 
tilting took place in relatively recent times, and after a period 
of elevation during which the streams had steeper slopes than 
they at present exhibit. 
I venture to suggest that the uplifting probably took place 
during the period of retreat of the New England glacial sheet, 
and before the ice had passed away from the northern part of 
the continent, and that the down tilting occurred when the ice 
had been in good part, if not completely, removed from the 
northern regions. It seems to me not improbable that the up- 
ward movement which followed the retreat of the ice was due 
to the removal of its weight from the surface of the continental 
arch. Assuming this to have been the case then we can easily 
imagine that in the region which was at a certain distance to 
the south of the retreating glacial escarpment would be tem- 
porarily elevated by the counter thrust arising from the weight 
of the neighboring ice. We may aid ourselves in forming this 
conception by the somewhat similar case.in which the surface 
of a peat bog rises above its original level around the part 
which is weighted down by the filling of a roadway. It is easy 
to see that if we should remove the weight which produces the 
counter-thrust the elevated surface would tend to resume its 
original level. 
We may thus conceive the succession of movements which 
have led to the present condition of our streams flowing from 
north to south, as follows, viz: 1st. The subsidence of the 
land surface under the weight of the ice to a depth below the 
level of the sea. 2d. With the retreat of the ice, a reélevation, 
in asudden manner, to a height much above the level of the 
sea. 8d. With the disappearance of the ice from the continent 
a readjustment of its position and a consequent lowering of the 
southern portion of the glaciated area. It is not likely that in 
the readjusted condition of the continent all parts are equally 
elevated or equally lowered. The present levels of the sev- 
eral divisions of the continental area would probably be deter- 
mined by complicated equations of thrusts, and it is probable 
that in this way we may explain the fact that certain of the 
lesser valleys of New England show little effect from the tilting 
movement which in immediately contiguous areas has had a 
great influence in the flow of the streams. I have observed the 
fact that in the hills of Mt. Desert we have evidence which goes 
to show a rising of the shorelands from the sea by a succession 
