138 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 



eluding that the river channel was carved in pre-Lahontan times, and also 

 that the lake which occupied Eagle-Carson Valley must have ovei-flowed and 

 cut down its channel of discharge so as to drain that Lasin to the bottom 

 previous to the existence of Lake Lahontan. We make this departure from 

 our immediate subject for the purpose of showing that the sediments of the 

 Eagle-Carson Lake, in which a variety of foot-prints have recently been 

 discovered at the Nevada State Prison, are older than Lake Lahontan, and 

 probably belong to early Quaternary or late Tertiary times. 



EXPOSURES IN THE CANON OF WAEKER RIVER. 



The Walker River, in its course between Mason Valley and Walker 

 Lake, flows through a comparatively narrow valley, which was deeply filled 

 with Quaternary lake sediments and is now a desert, sage-brush-covered 

 plain, dissected through the center by a canon eroded by the present stream 

 since the evaporation of the former lake. Like the Humboldt, the Truckee, 

 andtheCarson, the Walker River has exposed sections of Lahontan sediments, 

 in which the tripartite division is well displayed. As in the former instance, 

 the upper and lower members are fine, evenly laminated, marly-claj's, which 

 were evidently accumulated in quiet waters, andjare separated by a hetero- 

 geneous accumulation of sand and gravel that Vecords an interval of low 

 water. 



The tendency of current-borne debris to accumulate in narrow straits 

 connecting broad water-bodies has already been discussed in connection with 

 the descriptions of the gravel deposits observed in the Humboldt and Truckee 

 canons. A gravel embankment similar to those already described occurs a 

 few miles northward of Walker Lake and forms the divide between Walker 

 Lake and Walker River valleys. In this instance a large embankment was 

 built completely across the mouth of the narrow strait that formerly con- 

 nected the open waters of Walker Lake and Mason valleys; subsequently 

 this structure was cut through by waters flowing from the northward, thus 

 revealing a section of the inclined and arched strata in which the gravels 

 were deposited. 



A generalized section compiled by Mr. W J McGee, from many detailed 

 observations, is reproduced in Fig. C, Plate XXVIII, which represents the 



