CHAPTER IV. 



PHYSICAL HISTORY OF LAKE LAHONTAN. 

 Section 1.— SHORE PHENOMENA IN GENERAL. 



The examination of the shores of recent and fossil lakes has shown 

 that there are a number of characteristic topographic features, resulting 

 from the action of waves and currents, which are of geological interest, and 

 frequently enable one to determine much of the history of a lake that has 

 passed away. The dynamics of lake waters may be studied in any exist- 

 ing lake, but the topography of shores is best seen in lake basins that have 

 been emptied of their waters at a recent date. 



If we stand on a shelving lake shore during a gale that is blowing 

 landward, and watch the waves breaking on the beach, it will be noticed 

 that they apparently become accelerated on entering shallow water, and, 

 as their crests break into foam, they rush up the beacli or shore-terrace, 

 carrying stones and pebbles with them. As each wave retires we may hear 

 the sharp rattle of this material, even above the roar of the watei's, as it rolls 

 and slides down the beach, onl}- to be caught up by the next inrush, and 

 the process repeated again and again. Outside the line of foam fringing 

 the shore the water is frequently discolored, perhaps for several rods, by 

 suspended sediment derived from the comminution of shore debris ; farther 

 lakeward the waves are clear and blue, or perhaps streaked with long lines 

 of foam. The most superficial observations tend to assure us that vast 

 ■quantities of stones, pebbles, sand, and silt are constantly carried up and 

 ■down lake beaches and become rounded and smoothed by the process. 

 This conclusion is also sustained by the worn appearance of the debris on 



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