38. BOTANICAL GAZETTE [JANUARY 
gest and deepest of the group. It is not connected with the other 
two, a low, gravelly ridge separating it from the marsh just east 
of the woods, through which the other outlet flows. The outlet 
of this third lake flows through a bog at its western extremity, 
then to the southwest, where it makes a great bend through a 
level plain; then, after two or three miles, it turns north again, 
joining the outlet of the other two and forming a branch of 
Honey Creek which empties into the Huron River about a mile 
above Foster’s. 
The levels of these lakes are approximately the same, 7. ¢., 914" 
(278™) above sea level or 33% (10™) above the bench-mark on 
the library building of the State University, and 120% (36.5™) 
above the Huron River at the outlet of Honey Creek. The sum- 
mit of the divide east of the first lake is 955 (291™) above the 
sea, or 41" (12.5™) above the lakes. The corner on Liberty Street, 
one mile south of Huron is 979% (298™) and the kame just 
south of Liberty Street rises probably 75* (23™) higher. It was 
once proposed to derive the water-supply of Ann Arbor from the 
third lake, pumping the water fo a reservoir on top of this kame, 
about 140% (42™) above the lake. 
Ordinarily the level of the three lakes remains nearly constan 
throughout the year, becoming, however, 6 to 8™ (15-20) 
higher in the spring. In the fall of rgo1 the lakes were said to 
be lower than they had been in years. It is popularly supposed 
that they are fed by springs, but careful testing with a ther- 
mometer, in the fall of the year, has thus far failed to detect the 
influence of such springs. It is a very common thing, however, 
for lakes of this sort to be sub-irrigated, that is, water percolat- 
ing through the stony clay of adjacent hills makes its way to the 
lake, and, owing to the higher water-table on all sides, maintains 
the level constant in the lake basin. Another thing which helps 
to retain the water is the fact that the bottom of the lake basin 
is filled with a deposit of blue clay which prevents leaching. 
The depth of the lakes varies with the size, the first being 18* 
ei vai the second over 35% (10.5™), and the third 55* 
16.75"). 
This group of lakes is of glacial origin, like numerous other 
