140 



notes taken the greater number would be tedious and uninstructive to the 

 reader. The value of this work was evident, however, during every suc- 

 ceeding stage of the work; for during all the subsequent observations 

 of the lake, every detail of the shore was familiar as nothing else could 

 have made it, and objects could be oriented at a glance from any position 

 in the lake. 



Of the many things that might be said in detail concerning rhe physiog- 

 raphy of the lake only a few of the most important and striking, as char- 

 acter of soil along shore, etc., can be noted. 



SOIL OF SHORE. --Various parts of the shore, as along the Assembly 

 grounds, at the Biological Station, and south of Chicago Hill pier, are 

 sandy beach. This sand is not like that of the sand hills; it is a solid, 

 whitish sand, with small banks or streaks of quite reddish sand here and 

 there. Other parts of the sliore are of a tough, blackish or brownish muck; 

 the -greater portion of the shore is of this nature. The shore about Yar- 

 nelle's point is rather coarse gravel. 



Some parts of the shore are suffering wave erosion. Particular ex- 

 amples of this are the region just south of the mouth of Oheriy Creek, and 

 again at the cape just beyond the neck of the lake, and on the southern 

 side. At these places the lake has encroached a good deal on the land in 

 spite of the protection afforded by the roots of bushes, etc. Ti'ees and 

 bushes are undermined and fall ovei-, and there are stumps in the lake 

 bottom for some way out. At other ])laces, as at the south end of the 

 lake and along parts of the north end, tlio treeless, mucky shore is being 

 worn away. Here the waves act as a "horizontal saw" (to use Le Conte's 

 illustration I. leaving a solid, mucky platform in the bottom and a steep, 

 almost vertical step off" at the water's edge from the level plain to the 

 bottom. The Avaves often cut between tussocks of grass and leave minute 

 fiords. At othei- places the sod or turf is undermined, and moves up and 

 down with tlie waves. The muck is in places very tough and resisting. 

 Large chunks of the fibrous soil are torn loose from the shore or bottom 

 and rolled by the waves into a peculiar rounded form, much like a rounded 

 rock in shape, and yet not torn apart. The work of erosion along these 

 mrclcy stretches of shore is hastened and assisted very materially by 

 holes, presumably water-dog burrows, which honeycomb the soil and ren- 

 der it susceptible of being broken up into pieces. 



Elsewhere, especially between the patches of Scirpns lacustris to be 

 described later, sedimentation is going on qiiite rapidly, and banks of soft. 



