666 PROCEEDINGS OF THE CORDILLERAN SECTION 



the valley northeast of Peaviiie mountain and running north in Long valley to 

 the neighborhood of Honey Lalve valley. It is very probable that many of the 

 valley areas in which the beds are not now exposed really carry them overlain 

 by Quaternary deposits. In several such places this has been demonstrated by 

 shallow railroad grades, trenches, and wells. 



These beds lie unconformably on the granites and other members of the 

 Bedrock series, and consist largely of poorly cemented sands and clays, the 

 former being sometimes gray and friable, sometimes charged with limonite. 

 and occasionally nodular. The lateral corrasiou of the Truckee river a few 

 miles above Reno causes occasional landslides, that produce cliffs several hun- 

 dred feet high, exposing beautiful sections of the stratification (plate 73). 



Diatomaceous earth, frequently of great purity, is a characteristic member 

 of the series and just west of Reno is about 400 feet thick. Besides diatom 

 remains, it contains sponge spicules and a slight amount of mineral fragments. 

 Fish remains are found in it east of the Virginia range. Some layers are ashy 

 and carry small fragments of pumice and crystal (apparently pyroclastic) 

 fragments of minerals of igneous rocks. 



Current-bedded gravels, tuffs, and blue tuffaceous sandstones are common, 

 especially in the lower part of the series near Verdi. We also find fossil 

 leaves and lignite beds, the latter formed by leaf and twig accumulations (that 

 is, drifted material ) often intimately associated with laminne or with a general 

 admixture of volcanic ash. A shell limestone was observed in the Kawsoh 

 mountains near Hazen. 



These beds lie on the weathered surface of the andesites, but they precede 

 the block faulting of the ranges, some areas being found in the valleys and 

 some in the siimmit region of the Virginia and other ranges. They are charac- 

 teristically disturbed by tilthig and some folding, though except along fault 

 planes they generally lie at moderate angles of dip, say from 10 to 40 degrees. 

 The plant remains are of the broad leaf type (or reeds) and point to a lower 

 altitude of the country at that time, niese various relationships indicate that 

 the beds may be upper Miocene or Pliocene. 



An interesting section of the basal beds occurs a mile or two southwest of 

 Reno. The lava dips under the sediments and carries a layer of pre-Truckee 

 soil. The sediments show several alternations of distinct lake sediment and 

 alluvial material or wash, each a few feet or yards thick. This seems to indi- 

 cate a lake with considerable fluctuation in areal extent, and possibly therefore 

 occupying an interior basin without outlet (at least part of the time) similar 

 to the Quaternary Bonneville or Lahontan. 



The eastern part of the Truckee region and the Humboldt region are charac- 

 terized by thick rhyolitic ash accumulations. They may in part have accumu- 

 lated subaerially on desert valleys, Mit in part were deposited in water and 

 carry sand and pebble beds. Whether these should be associated with the 

 Truckee beds or separated as a later series has not been determined. 



Post-Tertiaky okogenic Movements 



At the end of the Tertiary or early in the Quaternary the acute deformation 

 took place that gave rise to the present mountain ranges. Folding or bending 

 movements were restricted in occurrence, the most chai'acteristic movements 

 being those of block faulting of the Basirf Range type. Most commonly the 



