252 C. Stock — Cenozoic Mammalian Remains 



earlier Tertiary sediments and lavas, but they were laid down 

 before the down cutting of the latest sharp gorges, for they 

 stand as the walls of these. They lie against the Carboniferous 

 limestones, and, as described by Marvine, against the Archean 

 granites along the Grand Wash. ' ' 



The basis for determination of age of the horizontally 

 bedded sediments as Pliocene is given by Spurr in the 

 following statement: 



"According to Dutton (Second Ann. Rept. U. S. Geol. Surv., 

 p. 67) the greater part of the general denudation of the Colorado 

 drainage region was probably accomplished in Miocene time, 

 whereas the cutting of the Grand Canyon probably began in the 

 early part of the Pliocene. The conglomerates and sandstones 

 under consideration were evidently deposited just before the 

 period of rapid canyon cutting, and this, in conjunction with the 

 evidence afforded by the underlying unconformable Tertiary 

 rocks in Meadow Valley Canyon, may be sufficient grounds for 

 specifying their age provisionally as Pliocene. ' ' 



Everett Carpenter^ in a paper on the ground water in 

 southeastern Nevada discusses the Meadow Valley 

 region. Concerning the geology of Meadow Valley, 

 Carpenter states : 



' ' The valley fill consists largely of gravel, sand, and variously 

 colored clay. Its depth is probably great. There are good 

 exposures of the unconsolidated sediments in the valley, but no 

 fossils have been found to give a definite clue as to the age. The 

 three terraces on the alluvial slopes indicate that there have been 

 at least three epochs of accumulation, which alternated with three 

 epochs of erosion. The terraces and the erosional features in 

 general are very similar to, and probably were formed contempo- 

 raneous with, those in Las Vegas Valley, which are thought to be 

 Pleistoeene in age." 



In the course of completion of the present paper there 

 appeared an important abstract by Mr. C. R. LongwelP 

 of results obtained from a study of the geologic feature of 

 southeastern Nevada'in which particular attention is given 

 to the region of the Muddy Mountains. In the descrip- 

 tion of the Tertiary formations, Longwell notes the pres- 

 ence of an older and younger series. The latter deposits 

 occupy the intermontane valleys and are composed of 

 silt, clay and sand to a thickness of nearly 2000 feet 



' U. S. Geol. Surv. Water Supply Paper 365, pp. 50, 58-59, 1915. 

 ' This Journal, pp. 39-62, January, 1921. 



