1<»K)J Bruncken, Studies in Plant Distribution. 147 



cipally on the bank, but influencing both beach and terrace. Three 

 kinds of erosion must be distinguished : Lacustrine, pluvial and 

 rivuline. Lacustrine erosion takes place chiefly at the few prom- 

 ontory points where beaches are absent. Here the undercutting 

 by the waves causes the bank to be vertical or even, for short 

 periods, overhanging, and the recession of the easily eroded cliff 

 must be very rapid. Of far greater importance is pluvial erosion. 

 The rain and melting snow wash material down the steep slopes, 

 at a rapid rate. Thereby deep and narrow gullies are formed, 

 with more or less considerable alluvial fans forming at their lower 

 ends. Moreover, landslides occur with great frequency. As a 

 result, the top of the bank is usually perpendicular or nearly so. 

 But at least three fourths of its height is covered with a talus of 

 varying steepness, on which of course the erosion processes con- 

 tinue. The gullies have a tendency to develop at almost equal 

 distances ; the consequence is that the talus forms a series of 

 tongues, shaped like the roofs of houses with their gable ends 

 toward the Lake. This feature appears very conspicuous from 

 the board of a vessel some distance off shore. Often the top of 

 these tongues is flattened, and in many cases several of these 

 flat-topped tongues run into each other on account of insignifi- 

 cant development of the intervening gullies, thus forming a terrace 

 of considerable extent and comparatively long duration. 



Generally speaking, the topography of the bank is exceedingly 

 unstable, changing with every rain storm and every winter thaw. 

 The downwash of material upon the beach not only raises the 

 level of the latter, but also increases its fertility. This however, 

 is subject to-exception. Tn several places, especially where the 

 Hamilton shales are found, the downwash forms a hard crust on 

 the surface of the beach, exceedingly hostile to plant growth. In 

 other places there are similar crusts of conglomerate, the pebble 

 and sand-grains of the beach and the finer earth derived from the 

 bank being cemented by a deposit usually colored reddish by 

 oxides of iron. 



Some of the gullies gradually develop into ravines. The tran- 

 sition from one to the other may be put at the point where a per- 

 manent water course shows itself at the bottom. Springs of more 

 or less regular flow are very common along the banks, and their 

 water contributes much to the occurence of landslides. When a 



