100 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



been subject to repeated fluctuations of level. That such was its history is 

 also evident from the multitude of terraces still remaining as records of its 

 former changes. The Lahontan water-lines are lacking in strength as com- 

 pared, for example, with those of Lake Bonneville, the reason being in part, 

 evidently, that the ancient lake margins were precipitous thi-oughout a large 

 portion of their extent, and the water-surface was greatly broken by islands 

 and headlands which nuisi; have retarded the force of the waves and cur- 

 rents; but the main reason why the old shore lines are poorly defined is 

 that the lake surface was not held at any definite horizon for a considerable 

 time. The records of wave action still remaining are sufficiently distinct, 

 however, to be easily traced, except on some gently-sloping shores where 

 the waters were shallow, and at the heads of deep narrow bays where all 

 shore phenomena are frequently absent. In the Lahontan basin, as in all 

 fossil lakes, the elements of shore topography to which we turn for the 

 history of the ancient water-body are terraces, sea-cliffs, bars, embank- 

 ments, deltas, etc. 



TERRACES Al^D SEA-CLIFFS. 



The most common of the records inscribed on the borders of the La- 

 hontan basin are cut terraces. These may be traced throughout a very 

 large portion of the basin, but are most distinct on the borders of the larger 

 deserts. About the southern margin of the Carson Desert the ancient lake 

 was. limited by mountains of soft, volcanic rock, which yielded easily to 

 both wave action and subaerial erosion. The result is a group of Gothic- 

 like mountains rising from a broad, horizontally scored base. The contrast 

 between rain sculpture and wave-sculpture is here well marked. 



In traveling over the Central Pacific Railroad between Golconda and 

 Wadsworth, one is seldom out of sight of the long horizontal lines drawn 

 by the waves of the ancient lake on the shores that confined them. Rec- 

 ords of the same character may be traced continuously about the borders 

 of the Black Rock and Smoke Creek deserts, and are strongly defined along 

 the bases of the mountains overlooking Pyramid and Winneaiucca lakes. 

 They. are again plainly legible on the steep slopes bordering Walker Lake, 

 as may be observed by the ti'aveler over the Carson and Coloi-ado Railroad. 



