RESUME; OF SHORE TOPOGRAPHY. 99 



sea-cliff, the latter slopes downward and forms a terrace scarp. Their upper 

 limit is a horizontal line marking the level of the water at the time they 

 were formed; their surfaces slope gently lakeward. 



Built terraces are shelves of debris formed along shores and are usually 

 adjoined to or combined with cut terraces. As in the previous instance, they 

 are limited on their lakeward borders by terrace-scarps, and may or may not 

 occur at the bases of sea-cliffs. Their shoreward margins are horizontal. 



Sea- cliffs are scarps formed by the erosion of cut terraces; their bases 

 are horizontal and coincide with the upper limit of terraces. 



Barrier bars are ridges usually composed of water- worn gravel, depos- 

 ited by currents in shallow water at some distance from land. Their, crests 

 are horizontal, and mark the storm limit of the waves and currents that 

 built them. In cross- section they exhibit anticlinals of deposition. Aber- 

 rant forms are V-bars, J -bars, looped bars, etc. 



Embankments are deposits formed by the transportation of shore drift 

 along terraces and barrier bars, of which they are continuations, to locali- 

 ties where the water deepens. Like built terraces and barrier bars, they 

 are composed of water- worn debris, but are frequently of great size; their 

 tops are horizontal, and in cross-section they exhibit anticlinals of deposition. 



Deltas are accumulations of stream-borne debris deposited about the 

 mouths of streams that debouch into still water; topographically they are 

 semicircular or fan-shaped, and, Avhen seen in radial section, exhibit a tri- 

 partite structure. 



Since the present chapter was written, a graphic and comprehensive 

 summary of lake shore phenomena has been published by Mr. Gilbert in the 

 Fifth Annual Report of the United States Geological Survey, to which the 

 reader is referred for a more complete discussion of the geological effects 

 of waves and currents than is contained in the present sketch. 



Section 2.— SHORE PHENOMENA OF LAKE LAHONTAN. 



In considering the question of outlet in a previous chapter, it was shown 

 that the shores of Lake Lahontan are unbroken by a channel of overflow. 

 It was therefore an inclosed lake, and, like others of its class, must have 



