SECTIONS EXPOSED IN TRUCKEE CANTON. 133 



of the Truckee River, the three divisions of Lahontan sediments so easily 

 recognized in many localities are here indefinite. 



Continuing towards Pyramid Lake with our study of the exposures in 

 the river banks, we find the section changing in its details and losing the 

 complex character observed at Wadsworth. Beginning a mile or two below 

 the position of the section given in detail above, and continuing for four or 

 five miles down the river, the exposures are almost entirely of upper lacus- 

 tral clays, including a few irregular strata of current-borne material. This 

 is indicated by the following section observed on the west side of the river 

 about four miles below Wadsworth: 



Feet. 



1. .^olian sand 1 to 2 



2. Dendritic tufa in mushroom-foniis Itol.Ci 



3. Clay, fine, sandy, ferruginous 4 



4. Clay, compact, drab-colored 12 



5. Sand, fine, ripple-marked 1 



C. Clay, fine, evenly stratified 2 



7. Sand and gravel, current-bedded 1 



8. Clay, drab-colored 8 



0. Sand, ripple-marked 1 



10. Clay, evenly stratified, with some sandy layers; to river 100 



Near the locality where this section was observed, but on the opposite 

 side of the stream, the lower fifty feet of the canon wall are composed of 

 coarse gravel which evidently represents the middle member of the Lahon- 

 tan series; half a mile down stream, however, the entire section is as'ain 

 composed of lacustral clays. 



Other abrupt changes of this nature are common and seem to indicate 

 that the medial gravels occupy an old eroded channel in the lower clays, 

 which is crossed irregularly by the present stream channel. 



Continuing down stream, one finds good exposures of the upper clays 

 resting on coarse current-bedded gravels which are without question a por- 

 tion of the middle member of the series. The medial gravels are here 

 probably represented in part by a heavy deposit of reddish-brown debris, 

 somewhat coarser than the normal lacustral clays and having a close resem- 

 blance to the upper or flood-plain portion of the medial gravels observed 

 in the Humboldt section. On the east side of the river this deposit becomes 

 thinner as we follow it westward, and at length disappears in a thin wedo-e, 



