THE TOPOGRAPHY AND HYDROGRAPHY OF ILLINOIS XXXIX 



The LemnacecB are everywhere lodged in mats and windrows, and, 

 amidst their green, one occasionally catches sight of a bright cluster 

 of Azolla. The water is clear and brownish save where our move- 

 ments stir the treacherous and mobile bottom. We now enter a 

 second time the partially wooded country, and cross the submerged 

 ridge to the sandy eastern shore of Thompson's Lake. This ridge 

 is covered by submerged vegetation which has as yet attained but 

 little growth. The "breaks" of the startled fish show that we have 

 invaded favorite feeding grounds. The waters are evidently mov- 

 ing towards the river, and they bear the rich plankton of Thomp- 

 son's Lake, while their turbidity is doubtless increased by the 

 movements of the fish. Schools of young fry can be seen feeding 

 upon the plankton in the warm and quiet waters. Thompson's 

 Lake, the largest expanse of water in the neighborhood, is wont to be 

 rough in windy weather, but if the day be still we can see the rich 

 aquatic vegetation which fringes its margin and lies in scattered 

 masses toward its southern end. Its waters seem somewhat turbid, 

 but more from plankton than from silt, though the deep soft mud 

 which forms much of its bottom is easily stirred. The slender 

 transparent limnetic young of the gizzard-shad may be seen swim- 

 ming near the surface. There is a perceptible drift to the south in 

 the open lake, though this current is deflected by the elevated banks 

 of Spoon River towards the Illinois River, crossing the lower bottom- 

 lands above this region. If we push on through the fringing willows 

 at the south we find a series of open places locally known as "ponds." 

 The warm still waters are turbid in places from the movements of 

 fish, and at times we see the compact schools of young dogfish 

 (Amia calva) and, if we are late enough in the season, the myriads 

 of young black, tadpole-like catfish (Ameiurus), likewise in schools, 

 while young carp (Cyprinus carpio) are everywhere. The new 

 vegetation is already springing from the decaying and matted stems 

 of the preceding summer. Turning back towards the river we pass 

 through the heavy timber where the still brown water, cool and 

 clear, overlies the decaying leaves and vegetation of last season's 

 growth, now coated with the flood deposits of the winter. Emerg- 

 ing again upon the river channel, we may find a turbid yellow flood 

 pouring out from Spoon River, bringing down its load of drift and 

 earth, and marking its course down the stream as far as the eye can 

 see. | 



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"Contrast with the extent and variety of conditions at flood the 

 limitations placed upon the stream at low water. Instead of an 



