DISCREPANCIES IN CLASSIFICATION. 145 



presented on Plate XVIII. The embankments near the south end of Win- 

 nemucca Lake are described on page 120. The discrepancy in reference 

 to the nature of the gravel deposits bordering Humboldt Lake may be 

 seen by comparing the pages referred to above with the description given 

 on page 742 of Vol. II of the reports of the United States Geological Explo- 

 ration of the Fortieth Parallel. 



The entire area represented as Humboldt Pliocene, on map V of the 

 atlas cited, has been considered thi'oughout the present volume as of 

 Quaternary age, and as furnishing the most typical exposures of Lahon- 

 tan sediments, as will be seen by referring to the descriptions of the Hum- 

 boldt and Truckee canons. 



The areas colored as Lower Quaternary on map V, of the atlas named, 

 are mostly playa-deposits; while the areas designated as Upper Quaternary 

 are largely covered with alluvial gravel, especially near the mountains, 

 but in the broader valleys within the Lahontan area large portions thus 

 designated are floored with Lahontan sediments. In the present report 

 Upper and Lower Lahontan clays have been recognized; these might with 

 propriety be termed Upper and Lower Quaternary, but cannot be correlated 

 with the Upper and Lower Quaternarj^ of King. The exposures of upper 

 and lower Lahontan sediments are so limited, occurring mostly in canon 

 walls, that they could scarcely be represented on a map of the scale used 

 in that atlas, and if mapped they would not agree with the classification of 

 the Quaternary there used. As the facts are interpreted by the present 

 wj-iter, the lake beds' there mapped as Lower Quaternary belong to Upper 

 Quaternary, while the playas also mapped as Lower Quaternary are recent. 

 The alluvial deposits, there mapped as Upper Quaternary, are deep forma- 

 tions whose accumulation began at least as early as the Tertiary and has 

 been continued to the present time. Their surface layers are in part mod- 

 ern, but other areas have received no )-ecent additions and are superficially 

 Upper Quaternar}'. 



MoN. XI 10 



