TERRACES AND SEA-CLIFFS. 



103 



terrace of construction a few feet wide, resting on the broad lithoid terrace 

 30 feet below. Where the shore records are unusually well displayed, as 

 along- the western margin of Pyramid Lake and on the south side of the 

 Carson Desert, the lithoid terrace sometimes has a width of 200 or 300 

 feet. Resting on it we sometimes find two built terraces of gravel and rolled 

 stones, the water-line of one being the highest of all the shore records ; 

 the second is intermediate between the Lahontan beach and the lithoid 

 terrace. This arrangement is illustrated in the accompanying diagram, which 

 exhibits a generalized profile of the shore : 



h 



.^Mifilo ul" Litliuiil TL-mice uml Lalioiitaii lic-acli. 



The line ah represents the oi-iginal slope of the mountain side before it 

 was modified by the waves of the lake. The lithoid terrace ccl was first 

 formed, the outer edge being l)uilt of detritus. The magnitude and persist- 

 ence of this ten-ace indicate that the water stood for a long time at a nearly 

 constant level, allowing the waves to carve out a broad shelf from the solid 

 rock. As we shall see further on, the terrace became coated with calcareous 

 tufa, and its gravel was cemented into a conglomerate. At some later 

 period in the history of the lake the water rose and built the two small 

 embankments, or terraces, that rest upon it, but it remained at these hori- 

 zons only a comparatively short time. 



Besides the more definite and strongl}^ marked terraces to which we 

 have given names, there are a large number of less deeply engraved lines 

 on nearly every portion of the former shore. Each of these scorings, as 

 we well know, is the record of a pause in the fluctuations of the water sur- 

 face ; collectively they indicate numerous changes in the lake level. The 

 obscurity and want of strength in many of the terraces is no doubt due in 

 a great measure to the fact that the slopes on which they are traced have 



