THE WORK OF WAVES AND CUEEENTS. 105 



of the waves and currents in an inclosed lake, the surface of which must 

 have fluctuated with the seasons, and become of broad extent during long 

 periods of more than usual humidity, only to contract again and perhaps 

 be divided into separate water bodies with the return of arid conditions. 

 Hence the comparative indefiniteness of its water lines. In the case of the 

 ancient Utah lake the hoi-izons of the most strongly defined terraces were 

 determined by overflow ; the water surface was thus maintained at a con- 

 stant level for long periods, and the shore phenomena at these favored stages 

 became the grandest that have yet been studied. 



BARS AXD EMBANKMEMTS. 



The deposits in the Lahontan basin that owe their origin wholly to the 

 constructive action of waves and currents are far more important and in- 

 structive than the associated terraces, and are deserving of the most careful 

 attention. Accumulations of gravel in the form of bars and embankments 

 occur at many points along the ancient shores which we are studying, but in 

 many cases these structures are indefinite or complicated, and their bearing 

 on the history of the former lake is difficult to trace. We have therefore 

 selected a few of the more typical exam])les to serve as illustrations of the 

 various phenomena observed. The maps accompanying the following de- 

 scriptions were drawn by Mr. Johnson from plane-table surveys made by 

 himself, and are so truthful and graphic that they require but little interpre- 

 tation. 



EMBANKMENTS AT THE WEST END OF HUMBOLDT LAKE. 



Humboldt Lake owes irs existence to the damming of the Humboldt 

 River by extensive gravel embankments which were thrown completely 

 across its channel during the time that Lake Lahontan occupied the valley. 

 The topography about the west end of the lake is represented with accuracy 

 on the accompanying map, Plate XVIH, which embraces the entire breadth 

 of the former lake in this portion of the valley. The highest level of the 

 ancient water surface is represented on the map by a heavy broken line, 

 and appears in the topography of the couritry as a gravel embankment, or 

 a wave-cut terrace at the base of a sea- cliff that is sometimes a hundred feet 



