218 W.S. Shaler—F luviatile Swamps of New England. 
The amount of downward movement indicated by these 
remains of submerged land plants cannot well be less than 
fifteen feet. It may have much exceeded this amount. It is 
impossible to determine by the scanty remains of these sub- 
merged forests and swamps, which are disclosed along the shore 
line, just how high above the water the surface which they 
occupy stood before they were lowered beneath the sea. There- 
fore, although a certain amount of subsidence of the region ap- 
pears to be indicated by these submerged plants, the amount of 
the movement can only be determined by a careful examination 
of the valleys themselves. Fortunately the data obtainable in 
this manner seem to make an approximate determination of the 
point in question. The evidences of former erosion which 
these valleys afford shows us that at one time their rivers had 
a rate of flow comparable in a general way to that of the rivers 
which flow from north to south. The question is, how great 
a tilting of these basins would be required in order to bring the 
streams to their present condition of relative stagnation and 
permit the development of the swamps which now characterize 
their basins. After the careful study of these valleys, compar- 
ing them with those in other districts, I am of the opinion that 
the tilting need not have exceeded two feet to the mile to have 
effected the change, and that it might have been effected with 
a somewhat less amount of alteration in the inclination of the 
stream beds. The least amount which would satisfy the con- 
ditions would be a lowering of the inclination of the river beds 
by one foot to the mile. The greatest submergence which I 
have been able to prove from the evidence of buried forests is 
in the region about Boston harbor, where it appears to -have 
been somewhere about twenty feet, rather less than more. 
This evidence is derived from some roots of a species of spruce 
obtained in Cambridgeport at a depth of about seventeen feet 
below high water, and some traces of roots of trees in their 
natural position below the level of low tide mark in the portion 
of Massachusetts Bay near Lynn. Now, from the sources of 
the Concord river to its outlet into the Merrimac, is a distance 
of about thirty miles in a direct line, and by the sinuosities of 
the stream is about forty miles. We see, therefore, that the 
proved subsidence, since the close of the Glacial period, is 
hardly sufficient to account for the change in the condition of 
the river, though it represents at least half the amount neces- 
sary to bring about that alteration. 
The moderate amount of the subsidence which has led to the 
swampy condition of these valleys is furthermore indicated by 
the fact that when the tributaries of the embarrassed streams, 
themselves flowing from south to north, are so placed that their 
original descents were steep, they have not had their basins 
made swampy by the change of inclination. 
