419 
III. The comparatively shallow, weedy lakes, with maximum 
depths at gage 8 feet, Havana, of about 5 feet. The lakes of this class 
in which collections were made in 1914 and 1915 (Flag, Seebs, Stewart) 
represented a total acreage at the low water of 1901 of about 1,500 acres, 
and at 8 feet, Havana, somewhere near 4,000. All of these lakes went 
completely dry in seasons of extreme low water before 1900. Both in 
the shallower and the deeper portions the black bottom deposits con- 
tain a much larger percentage of partially decayed dead vegetation than 
is found in the open waters of the lakes of Class I. In recent midsummer 
seasons, up to 1914, Flag and Seebs lakes have been almost completely 
filled with growing vegetation. In Stewart Lake at the same time some 
open water was to be found in the central deeper portion toward the 
foot, but much less relatively to the total area than was the case in such 
lakes as Thompson and other deeper lakes of its type. 
IV. The very shallow, very weedy lakes, with greatest depths at 
the low water of 1910—1914 between 3% and 4 feet. These lakes 
(Duck, Dennis, Crane) were little more than lily or flag ponds before 
1900, going wholly dry at low water in most seasons before the opening 
of the Chicago Sanitary Canal. Between August and October, 1914, 
Duck and Dennis lakes were so filled with mixed vegetation that it was 
difficult to pass through them with a skiff, even the fallen dead stems 
of the coarse water-plants being blanketed with living filamentous 
algae. Crane Lake in 1914 and other recent years has been a vast lily- 
bed, with its rather more open, but densely shaded bottom sprinkled 
with dead lily stems and “yorkey-nuts”. These three lakes had a low- 
water acreage in 1901 around 1,200 acres. 
V. The shallow dead timber and brush areas first permanently 
submerged after the opening of the Sanitary Canal in January, 1900. 
These shallow backwaters, ranging in depth from 1% to 4 feet over 
most of their areas, have alternating opener and densely weeded 
stretches, the prevailing vegetation being Potamogetom and Polygonum. 
Their location on the ridges between such lakes as Flag and Thompson, 
and on similar ridges between these lakes and others and the river, 
makes them in reality littoral, either of the river or of lakes of the pre- 
ceding classes, as the case may be. Their bottom soil still contains 
abundant traces of the sticks and dead leaves contributed by the willows 
and mallows and button-bushes that grew there 20 years ago. The area 
represented by waters of this type can only, for the present, be roughly 
estimated. The total area under 4 feet in depth at the July—October levels 
of recent years between Copperas Creek and Lagrange dams (about 29,700 
acres) made up over 50% of the total ex-river acreage, while careful 
estimates in the case of Thompson Lake as flooded to the same elevation 
(approx. Havana 8 ft.) indicated that on that gage in this lake these areas 
made up about 30% of the total land flooded. The dead timber and brush 
areas studied by us in 1914 and 1915 were all in the vicinity of Havana 
and were variously contiguous with Clear, Flag, Thompson, Dogfish, 
and Quiver lakes. 
