132 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



been sheltered from erosion. The western bank of the Truckee just below 

 Wadsworth, and 2 or 3 miles from the gorge through which the river enters 

 the valley, is about a hundred feet high and exposes the following diversi- 

 fied sections: 



Feet. 



1. ^oliau sands ,5 to 18 



2. Sandy clay, line, evenly stratified 12 



;i. Clay, drab-colored, fiue-graiued, homogeneous 



4. Clay, evenly stratified, ferruginous 1. 5 



5. Saud, argillaceous, in contorted strata 3 



6. Sand, fine, clean, sharp 2.5 



7. Cl.ay , sandy, ferruginous, jointed 2 



8. Sand, coarse and pebbly 5 



9. Clay, argillaceous 2 



10. Sand, ferruginous 10 



11. Clay, drab-colored, with seams of tine sand 2 



12. Sand and gravel, micaceous 10 



13. Gravel, well rounded, with seams of sand and occasional boulders 



sometimes 2 feet in diameter 6 



14. Sand, evenly stratified, micaceous, ripple-marked 2 



15. Sand, sharp, clean, micaceous 12 



16. Sand, evenly stratified, micaceous, ripple-marked and current- 



bedded; pa.ssing into — 3 



17. Clay, fine, evenly stratified, drab-colored, sometimes sandy; jointed 



by two systems of fractures nearly at right angles, and resting un- 

 conformably upon — 6 



18. Gravel, well rounded, current-bedded, and containing boulders 2 feet 



in diameter ; to river 20 



110 to 123 



The numerous changes recorded by this section are no doubt to be 

 accounted for by the proximity of the former mouth of the river, from which 

 the greater part of the debris forming the beds was derived. 



A noticeable feature of the section is the fine exhibition of double 

 jointing to be seen in bed No. 17. This stratum is of compact and nearly 

 homogeneous, sandy clay, resting on a thick dejiosit of unconsolidated 

 gravel and bowlders, and overlain by similar material. As the inclosing 

 beds are too loose and incoherent to exhibit jointed structure it seems 

 evident that the forces producing the joints must have originated in the 

 clays themselves; for it is difficult to understand how external agencies, as 

 an earthquake shock for example, could have been transmitted through the 

 loose gravel deposits inclosing the clays. The jointed stratum to which 

 we have called attention apparently represents the lower lacustral clays, but 

 as the section is rendered abnormal by its proximit}^ to the ancient mouth 



