[PENHALLOwW] DEVELOPMENT OF CERTAIN MARSH LANDS 35 
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development until a second forest of white pine had attained to an age 
of one hundred years or more. 
The second crisis in the history of the bog was introduced at the 
time when the pine had reached the age indicated. The evidence of this 
appears in the abrupt destruction of the forest and the replacement of 
the normal land vegetation by halophytic types. The transition was 
abrupt as indicated by the clearly defined cleavage between peat derived 
from decaying leaves and other remains of land plants, and the forma- 
tion of a turf composed wholly of the remains of salt marsh grass and 
related types. We have here, then, the most positive proof of the 
sudden invasion of the area by the sea, and it remains for usjto deter- 
mine in what way this flooding was brought about. 
It has been noted that the obstruction of the southern channel by 
growth of vegetation, caused a damming back of the drainage water, 
together with the formation of an “inlet” in the barrier beach. This 
is a result which might be anticipated, and it is one not unfamiliar to 
us under other circumstances of location. Had the general region 
been in a stable condition, it is quite probable that nothing more than 
a drainage outlet would have formed. But the continual subsidence of 
the shore line introduced another factor of .great importance. The 
erosion caused by the overflow was supplemented by wave action, and 
these influences operating concurrently with subsidence, the outlet was 
cut down to a continually lower level until it reached the underlying 
rock where further progress was arrested. This is the condition at the 
present time, and the bottem of the “inlet” is now considerably above 
what we have reason to believe is the real bottom of the bog. 
The breaking down of the barrier beach led to the sudden overflow 
of the bog by salt water, by reason of which fact it was abruptly con- 
verted into a salt water marsh, and this has been its more recent history. 
One other aspect of these changes is to be found in the reopening 
of a channel to the southward, in the original location. It has been 
shown that a very narrow and very shallow channel at present admits 
an interchange of sea water with Chauncey Creek at high tide only. This 
channel occupies the identical position of the original outlet of the pond 
and of the bog in its earlier stages of growth. It is significant, however, 
that its depth is scarcely greater than the thickness of the salt marsh 
turf—that is, about three feet, and the extent to which it is carried 
below that turf is the result of natural erosion from the flowing tides. 
It is thus quite obvious that this channel has not only been opened 
within very recent times, but that its development is coincident with the 
growth of the marsh turf. From this it seems clear that it must have 
Sec. IV., 1907 
