[PENHALLOw] DEVELOPMENT OF CERTAIN MARSH LANDS 43 
nine inches in thickness. This was the product of not more than thirty-. 
five years possibly less, but the higher figure may be taken as affording 
a safer basis for calculation. Applying this fact to the Brave-Boat 
Harbor marsh, it will be seen that the salt marsh turf at that place may 
have been formed within a period of seventy years, and upon this basis 
it might be assumed that the pine forest previously existing there, had 
been destroyed by inundation of salt water about the year 1835. It is 
questionable, however, if the rate of growth observed at Kittery, about 
one-fourth of an inch per year—certainly not an excessive rate—will 
apply in all cases, and to establish an ample margin of safety, it may be 
assumed that the turf at York required a period of one,hundred years. 
Per contra, it should be kept in mind that this turf has developed 
at a rate equal to that at which the general area is subsiding, and on the 
basis of two feet per century, the whole marsh turf should have formed 
within a period of seventy-five years, a figure which is curiously like 
that derived from the known rate of the Kittery turf. 
Shaler (7) has furnished some data of great interest and value in 
this connection, and his statement should be presented in full. He says 
“The formation of swamps depends upon conditions which retain upon 
the surface a sufficient quantity of water to prevent the complete decay 
of the vegetable matter which may be accumulated upon it.” 
“ At the present rate of deposition of carbonaceous matter from 
decayed roots, fallen leaves, boughs and bark (which scales off from the 
trunks and branches), as well as the seeds of the trees, amounts, probably 
to sufficient material to produce, if it were preserved, as much as one- 
tenth of an inch each year over the whole surface occupied by woods. 
Thus ‘if the matter accumulated as it does in the swamp, ten inches of 
carbon would be laid down upon the surface in a century. One thousand 
years would produce over eight feet of such material.” 
“When for any reason the forest bed is more than usually wet, the 
process of interstitial decay is partly arrested, the accumulation of 
peaty matter begins, and in many cases, this process leads, by consider- 
able additions of the swamp deposits, to the destruction of the trees 
* which occupied the area. The accumulation of peaty matter will con- 
tinue until the gradient of the district rises and a more complete 
drainage is effected. Thus, owing to the drying of the upper part of the 
marsh, the further thickening of this material is arrested. In general, 
however. in all regions occupied by woods, the natural gradients are 
sufficient to keep the land dry enough to prevent the formation of 
swamps.” 
If now, we apply to the York marsh the rate of growth of one-tenth 
-of an inch per year as established by Shaler, it will be possible to show 
