DELTAS OF THE A^'CIE^'T LAKE. 123 



bodies. The embankment was built by currents from both the north and 

 the west, and was carried out over horizontal lacustral beds, as represented 

 in the sketch. 



The buttes in King's River Valley were islands in Lake Lahontan and 

 became surrounded by terraces, bars, and embankments that were built by 

 the currents sweeping past them. 



The topographic forms produced by the deposition of gravel in the 

 paths of currents are extremely varied, and usually present curving con- 

 tours and smooth, rounded crests, that are in marked contrast to the angular 

 mountain slopes rising above them. Wherever the current-built structures 

 of ancient lakes occur, one is sure to find an illustration of the striking 

 contrast exhibited by the angular reliefs produced by subaerial erosion, and 

 the rounded and flowing outlines resulting from the action of waves and 

 currents. Aside from the bearing that these gravel embankments have on 

 the geological history of the basin, one may always derive aid from them 

 in determining the action of currents in existing lakes. The hydraulic engi- 

 neer will do well to study the processes employed by nature to accomplish 

 results that are frequently analogous to the works desired by man for im- 

 proving navigation or providing a haven for shipping. 



DEILTAS. 



The study of the records left by Lake Lahontan has added but little 

 to our knowledge of deltas, for the reason that the lake was too inconstant 

 in level to favor their formation, and also because nearly all the tributary 

 streams entered the lake at the heads of narrow bays and estuaries, which 

 were imfavorable localities for the development of structures of this nature. 

 The Humboldt River entered the Lahontan basin at the head of a long, 

 narrow arm of the old lake, which became deeply filled with debris, but is 

 not now exposed in section. Farther southward in the same valley, between 

 Mill City and Oreana, the Lahontan strata are well exposed, and will receive 

 attention under the section devoted to sedimentary deposits. In the south- 

 ern portion of the section to be seen in the banks of the Humboldt River 

 there are inchned strata that have a striking resemblance to delta structure, 

 but after a careful examination it was concluded that they owe their inch- 



