TWENTY-EIGHTH ANNUAL MEETING. 25 
of the lake in 150 to 400 years. The narrowest marsh I have seen around a little 
lake 30 feet or upward in depth is about 150 feet in breadth; and if 7,000 years 
be taken as its probable duration, since the disappearance of the permanent ice, 
the lowest estimate would be about right. On the other hand, lakes one-half to 
one mile in extent and not over six feet deep have been entirely overgrown by 
marsh and are dried up. 
The thickness of the black vegetable stratum that covers any marsh varies, 
according to the depth of the original lake, from 2 to 10 or 12 or even 20 feet, 
where the lake is very deep. It takes a very long time for a thickness of two 
feet or more to form by the decay of the grasses and other marsh plants that grow 
there. After the marsh becomes firmly fixed to the ground, tamarack trees 
grow, and it becomes a swamp. 
Underneath the overhanging marshy covering at the edge of any lake may be 
found a certain depth of infusorial or calcareous earth. This forms around the 
edge of all marsh lakes. It does not keep pace in its growth with the growth of 
the marsh ; and if the edge of the lake where the shells may be found should be 
moderately deep, the shells are constantly falling through the ooze to the bot- 
tom, leaving the upper portion next to the marshy covering very thin and loose ; 
yet the growth of marsh surface continues, and when the lake is not deep its ex- 
tension toward the center is reasonably rapid. 
A Marsa Lake. 
A description of one of these lakes in this connection will be appropriate, as 
it is representative of a large class of very small lakes, all of which come under 
the rule as to closing: A small deep lake in the edge of the ‘short hills’’ and 
close to the great Shiawassee marsh hereafter described. It is known as Drew’s 
lake, and is nearly surrounded by hills 25 to 40 feet high. The lake is nearly cir- 
cular; diameter about 400 feet from marsh edge to marsh edge; depth at edge 
of marsh 15 to 18 feet ; depth in middle of lake about 30 feet. The water is quite 
clear, though slightly reddened as though it were a weak infusion of grass, tama- 
rack, and other leaves. There is no permanent inlet; there is a small sluggish 
outlet discharging about one-half cubic foot per second. Outlet is bordered by 
marsh land. 
Completely surrounding the lake is an annulus of marsh land 50 to 75 feet wide, 
covered with marsh grasses and sedges, with a few other marsh plants interspersed. 
Most of the surface of the marsh is one or two inches above the level of the water ; 
though there are spots one or two inches below the surface of the water. Such 
spots are covered exclusively with a small species of Hleocharis (possibly #. ten- 
uts ), perhaps several species. 
Near the outlet and at one other spot which approximates a temporary inlet, 
there are boggy tracts in which the grass grows only on the tops of ‘‘bogs.”’ 
These ‘‘bogs’’ are tufts of peat about 8 to 12 inches across and 10 inches high, 
broadest at the top, and 4 to 10 inches apart. They are level on top and uniform 
in height, with perpendicular or concave sides. Water flows sluggishly at times 
in the interstices between the bogs. There is no vegetation between the bogs, 
except in the drier places a little sphagnum. 
The marsh floats. Thickness at its edge about 30 inches; depth of underly- 
ing water about 14 feet; one or two feet deeper in high water. Thickness or 
depth of marsh 50 feet back from the edge, 6 feet; depth of underlying ooze 
about 8 feet. Measurements were taken with a smooth, sharp-pointed tamarack 
pole. The relative depths of humus and underlying ooze could only be deter- 
mined by the difficulty of pushing the pole down. As soon as the peaty stratum 
was penetrated the pole would go down easily. The pole brought up adhering to 
