170 BOTANICAL GAZETTE [SEPTEMBER 
The mode of formation of the marshes. 
So much for the origin of the marshes as a whole; we con- 
sider next the actual process of marsh-building by the sea. It 
may best be observed along the tidal rivers, which play an indis- 
pensable part in the building of the greater marshes. At ordi- 
nary tides the rivers do not overflow their banks nor reach the 
dikes at all. But at the spring tides every month they rise 
higher, the waters rush more swiftly, and, gathering up yet more 
mud from banks and bed,?° overflow the banks, and, unless 
stopped by the dikes, spread abroad over the marshes. When 
the water thus leaves the channels, however, its speed is at once 
checked, and soon it comes to entire rest: it can no longer carry 
its burden of mud, and drops most of it. The water leaves the 
rivers so muddy one can see scarcely an inch or two into it; it 
returns, a few minues later, fairly clear. The thickness of mud 
deposited at a single tide varies from a small fraction of an inch 
on the higher places, to several inches on the bottoms of lakes 
which have been opened by canals to the tide. 
The powerful tidal currents in the crooked rivers cause con- 
stant and rapid changes in the soft muddy banks, and all the 
phenomena of the wandering of rivers in a flood plain may here 
be seen upon an unusual scale. In fact the marshes are really 
the flood plains of the tidal rivers, though built by materials 
Acadia (as shown in Bulletin of the Natural History Society of New Brunswick 
4339); and second, everywhere outside of the longest-built dikes the marsh is 
built up higher, even to two feet or more, than it is inside the dikes. Since the marsh 
was built as high as the tides could reach before it was diked, the land must have sunk 
to allow it to build so much higher now, even allowing for some sinking of the marsh 
through the removal of its mineral matters with the crops. Further, the ease with 
ditch diked upon both sides was neglected, when it filled itself up with mud toa 
height of two feet above the surrounding marsh. 
*° The percentage of mud in the water is not so great, however, as it appears and 
as popularly supposed. To the eye it seems often to be little more than “liquid 
mud.” By use of a graduated measuring glass on the end of a long cord I have taken 
samples from the bridges at various places, which, after settling, allowed the percent- 
age of mud to be determined exactly. Ihave found the greatest amount in the rivers 
emptying out at low water, when it rose to an extreme of 4%, and it ranged at other 
times and places from that downward. At flood tide I have nowhere found it reach- 
ing 2%. 
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