DISTRIBUTION OF MATERIALS 497 



channel in the cliff, running back nearly 100 feet, and at the present time 

 the cliff has retreated at least 6 feet since the burrow was opened out. 

 The materials at this point happened to be hard glacial till. Had they 

 been soft sand, the destruction in the time which has elapsed since the 

 burrow was opened would have been much greater. 



The farmers plowing their land close to the edge of the cliffs, partic- 

 ularly when the furrows are made at right angles to the shoreline, break 

 the protecting vegetable covering and binding roots and open up just 

 so many potential channels, this being particularly true if the soil is 

 sandy. There are numerous instances to be seen along the shores of both 

 lakes where deep notches have been cut in the cliffs and where channels 

 run back inland, in some cases as much as half a mile, which have been 

 started by carelessness or by ignorance in the matter of a proper method 

 of plowing. 



A considerable amount of material, particularly of the finer sorts, is 

 brought down to the lake shore from the interior by the streams and 

 rivers. In times past the amount must have been very large, if one may 

 judge by the size and form of the valleys the tributary streams have 

 carved in the glacial deposits across which they drain. At present dur- 

 ing the greater portion of the year the amount of material transported 

 is exceedingly small and the total amount contributed by the streams to 

 the shore waste is, compared with that derived from the immediately 

 adjacent land, relatively insignificant. 



Distribution of the Materials on the Shores 



The waste supplied to the shores from different sources is spread out 

 in a nearly even sheet parallel to the shoreline; much of the finer ma- 

 terials are carried out rapidly to the deeper waters and there deposited, 

 while the sands and coarser materials are shifted along the shore within 

 the limits of the wave-swept zone. The active agency in this distribu- 

 tion is the waves and the longshore currents, which are always associated 

 with them. Most of the active transportation takes place during the 

 time of the greater storms; during a period of light winds only sands 

 and finer gravels are moved. Probably the greatest amount of trans- 

 portation is during the period of autumn storms, though a very consider- 

 able movement takes place also in the spring. During the summer 

 months, except when there occurs an unusual and heavy storm, trans- 

 portation is very slight. During the winter months, when the shores 

 become lined with ice, often forming cliffs 6 to 15 feet in lieight and ex- 

 tending out into Avater about 4 and occasionally more feet in depth, trans- 

 portation is at a minimum. 



While the winter ice protects the shore for a time from the action of 



