696 The American Naturadist. [August, 
lake by evaporation. On the shores of these lakes would be 
afforded a congenial place for the first plants, among which, no 
doubt, sphagnum was prominent. The available food supplies 
in the soil of the hills around was washed and afforded food 
for these plants. As plants grew upon the hills, vegetable 
humus accumulated, and the wash from this further enriched 
the soil at the shore. But while this washing contributed 
something to the accumulations of the swamp, it, under no 
circumstances, can be compared to the soil washed down upon 
the flood plains of upland streams, and for the reason that 
these streams are not rapid enough to carry much solid ma- 
terial. The accumulations in the swamps are almost entirely 
the decayed plants that have grown there. 
ABILITY OF THE LAKE TO RESIST INVASION. 
The factors which determine the ability of the lake to resist 
invasion are its depth and the character of its shores. If the 
conditions are right, a lake even of considerable depth will be 
steadily encroached upon by vegetation. On the other hand 
a shallow lake will grow over much more rapidly. There is 
a popular notion that a cranberry bog may grow right over a 
lake, and that the flexible turf is like a blanket spread over 
the surface of the water. Walking on these places certainly 
gives one that impression. I have never seen a case where 
this was the actual condition of affairs. If you penetrate the 
turf anywhere you will find the blackest and softest kind of 
mud, almost as mobile as water, but as a plant food much 
more nutritious. From a boat there sometimes appear deep 
recesses far under the turf, but these are more apparent than 
real. There are often recesses under the turf, just as there are 
under harder shores, but these are not deep, and I feel reason- 
ably sure that the floating moors float upon mud rather than 
upon water. 
THE EFFECT OF WIND UPON THE RELATIVE POSITION OF LAKE 
AND BOG. 
The position of the lake, with reference to other parts of the 
swamp has attracted my attention for some time. The lakes 
in the northern and western parts of Oswego County have, aS 
