487 
lands above. The elevated deposits of Spoon River and the 
consequent crowding of the channel of the river to the east 
bluff at Havana force all of the water of overflow (at stages 
below about 16 feet) to seek the main channel. The configura- 
tion of the low-lying bottoms above is such (see PI. II.) that 
the lakes in question form natural channels for the movement 
of a large body of impounded water. This movement is well 
marked at stages above eight feet. So far as 1 am able to judge 
from field observations, the current conditions in Thompson’s 
Lake and the Dogfish-Quiver area are not greatly different. 
The current continues in both lakes as levels fall to six feet, at 
which level Thompson’s Lake loses its connection with the 
river through the “cut road” (PI. II.), and movements in it 
at lower levels are confined to those due to ingress and egress 
of water through the slough, and are consequently inconsider- 
able. On the other hand, Quiver Lake continues to be traversed 
by the discharge from Quiver Creek, and our collections were 
usually made in the channel in the vegetation. In Dogtish 
Lake at low stages there is no current traversing the lake. 
Phelps Lake hes at so high a level that only the floods exceed- 
ing eleven feet bring it into connection with the general cur- 
rent of overflow, which in this case generally comes from 
Spoon River. Below this level the only movement in its water 
is the gentle one due to the receding flood. So far, then, as 
the current is concerned, it is a common though not equally 
distributed factor at high-water stages in all areas compared, 
while at low water it is an important feature in the environ- 
ment in Quiver Lake but is practically absent in the other 
three localities. This fact undoubtedly accounts /” part for the 
barrenness of the waters of Quiver Lake (1.53 em. per m.*, or 
only .55 for the average of low-water periods—i. e. below 5 ft.) 
as compared with those of Dogfish (4.22), Thompson’s (8.15) and 
Phelps (19.44) lakes. This current does not, however, traverse 
or appreciably affect the waters of Dogfish Lake, and their bar- 
renness still remains for contrast with the productiveness of the 
vegetation-poor waters of Thompson’s and Phelps lakes. 
