351 
IV., XV., XVI.). The northern end of the lake is Y-shaped, 
and the western arm is known locally as Dogfish Lake. 
The lake from Quiver Creek to its mouth near Spoon River 
is about 3 miles long, and does not exceed a quarter of a mile 
in width at any point. The lake proper, that is, above the 
chutes and excluding the western arm, contains at low water 
about 230 acres (93 hectares), but approaches 500 acres if these 
contiguous bodies of water be included. As levels rise, its area 
increases rapidly, and at 6 to 8 ft. the demarcation between 
river and lake is obliterated, and extensive areas to the north- 
ward (Pl. II.) come into connection with it, while at higher 
levels it quite loses its identity as a separate area (PI. IIL.) ex- 
cept as the tree tops and its clearer waters serve to differentiate 
it from contiguous channel waters. Its depth at low water 
(river levels about 2 ft. above low water of 1873) is throughout 
most of its area less than 2 ft., and in the deepest parts, at the 
narrows above the chutes, it does not exceed 4 ft. 
The bottom is of hard sand and bluish clay covered gener- 
ally by a soft alluvial ooze of 1 to 2 or more feet in depth. Its 
eastern bank is a sloping sandy bluff (Pl. XV.), which abounds 
in clear springs of cold water, occurring the whole length of 
the lake and contributing nota little to its water supply. The 
western bank is of black alluvium, and the ooze along its mar- 
gin of considerable depth. The eastern arm of the lake receives 
Quiver Creek, a tributary draining 220 sq. miles of sandy upland 
and “second bottom.” 
The vegetation, described on page 244, in low-water condi- 
tions frequently chokes the channel, which extends from the 
mouth of Quiver Creek in a tortuous course through the vege- 
tation along the western shore of the eastern arm towards the 
point between this and Dogfish Lake, and thence in an equally 
crooked and shifting course towards the mouth. 
It was in this channel in low water, and in its neighbor- 
hood at times of high water, that our plankton station was lo- 
cated (Pl. II). It is simply a shifting path through the vegeta- 
tion, and is not generally marked by deeper waters than adja- 
