88 GEOLOGICAL HISTOEY OF LAKE LAHONTAK 



every shore. A little attention also enables one to ascertain that the beach 

 material greatly assists the waves in cntting- away the coast so as to form 

 terraces and sea-cliffs, and is subsequently utilized in building bars and 

 embankments. The modifications of lake shores due to chemical action 

 need not receive attention at this time. 



The principal features entering into shore topography are terraces, 

 sea-cliffs, bars, embankments, and deltas. These, as will be shown below, 

 result from the action of waves and currents on the shores that confine 

 them, and differ so widely from the topographic forms produced by sub- 

 aerial erosion and other geological agencies that the nature of their origin 

 may be determined at a glance. 



TERRACES. 



The most characteristic forms resulting directly from wave action are 

 sloping terraces l^ounded by a steep scarp, termed a sea-cliff, on the land- 

 ward margin, and a second scarp, less abrupt, on the lakeward border. 

 These forms are illustrated in the following diagram, which represents the 

 profile of a lake shore so carved by waves as to form a cut -terrace and sea- 

 cliff. The line ah represents the original slope of the shore before its mod- 

 ification by waves; ac the profile of the sloping terrace ; and cb the sea-cliff. 



Fin. 8.— Ideal profile of a cut-terrace. 



In the desiccated lake basins of Utah and Nevada terraces of this natui-e 

 frerpiently occur that are hundreds of feet in breadth and overshadowed by 

 cliffs which at times are a thousand feet high. 



The material derived from the formation of a cut-terrace at first encum- 

 bers the shelf formed, but is soon removed by the waves and currents and 

 its place supplied b}^ fresh debris. The finest of the waste from the hind is 

 carried lakeward by the undertow and finally deposited as lacustral beds; 



