abstracts: geology 95 



calcareous shales of Upper Cretaceous age. They resemble them in 

 one fundamental respect, however, in that they were formed later 

 than the strata that inclose them. 



GEOLOGY. — Geology and water resources of Big Smoky, Clayton, and 

 Alkali Spring valleys, Nevada. Oscar E. Meinzer. U. S. Geo- 

 logical Survey Water-Supply Paper 423. Pp. 167, with maps 

 and other illustrations. 1917. 



This paper describes in detail three typical desert basins of the 

 Basin-and-Range Province, with respect to their physiographic devel- 

 opment and the absorption, circulation, and discharge of their ground 

 waters. 



Two cycles of erosion are shown in the Toyabe Range by two strongly 

 contrasting types of topography. After the region had been eroded to 

 a stage of maturity, probably late in the Tertiary period, it was faulted 

 and uplifted, and the resulting escarpment was attacked by the streams, 

 producing a very rugged front. Extensive faulting, continuing until 

 recent time, is shown not only by precipitous mountain fronts but also 

 by observed displacements, by poHshed surfaces, and by numerous 

 escarpments in the valley fill. Evidences of glaciation, previously 

 reported, are believed not to exist. 



Elaborate systems of beach ridges or embankments, the largest 

 nearly 50 feet high, mark the outKnes of two Pleistocene lakes, desig- 

 nated by the author as Lake Toyabe and Lake Tonopah. Lake 

 Toyabe, when at its highest level, was about 40 miles long, 9 miles in 

 maximum width, and covered an area of approximately 225 square 

 miles, or 18 per cent of the drainage basin in which it lay. Lake 

 Tonopah, when at its highest level, was about 22 miles long, 5^ miles 

 in maximum width, and approximately 85 square miles in area, or 

 only about two-fifths the area of Lake Toyabe. This area was only 

 4.2 per cent of the to^al drainage basin tributary to the lake — a per- 

 centage less than one-fourth as great as that of Lake Toyabe. 



The most important contribution of the report is a quantitative 

 discussion of the origin, absorption, circulation, and discharge of the 

 ground water, and of the criteria for determining areas of ground-water 

 discharge. The amount of absorption was estimated chiefly by meas- 

 uring stream flow at successive points on a part of the 54 small streams 

 that discharge into Big Smok}^ Valley, and deducting for evaporation 

 and transpiration from the wetted areas. The total annual supply of 

 ground water was estimated to be several tens of thousands of acre- 

 feet. The criteria for determining areas of discharge are (1) the mois- 



