1914] Buwalda: Tertiary Mammal Beds in West-Central Nevada 347 



varying amounts. The color of these pyroclastic materials ranges 

 through white, gray, red, and brown. Rapidity of accumulation is 

 implied by their often being indistinctly bedded or massive in thick- 

 nesses of thirty to forty feet, and by the usual absence of foreign 

 material. Sharp boundaries usually mark off these tuff strata above 

 and below, indicating suddenness in commencement and in cessation 

 of tuff deposition. From these facts it seems probable that volcanic 

 activity occurred in the region during the deposition of the Esmeralda 

 strata, 



Certain strata in the section are quite certainly of terrestrial origin. 

 Such are certain beds consisting of coarse, unassorted, angular mate- 

 rials, derived from the rocks of the nearby ranges, and embedded in 

 a matrix of tuffaceous or arkosic materials. These strata have all the 

 characteristics of fanglomerates as that term has been defined by 

 Professor A. C. Lawson 8 to designate alluvial fan deposits. These 

 fanglomerates are intercalated with the lacustral beds and probably 

 were deposited during periods of contraction of the lake area, Their 

 presence has a bearing on the question of the climate prevailing in 

 this region during the lacustral period, inasmuch as fanglomerates are 

 rather characteristic of arid conditions. 



A few thin beds of fine, well-rounded gravels, perhaps of fluviatile 

 origin, were noted. 



Thickness. — A section of the Esmeralda beds measured on the 

 road between Mina and Cloverdale immediately east of Cedar Mountain 

 shows a thickness of about seven hundred feet. As this section is 

 at the border of the lacustral series, it consists for the most part of 

 coarse, detrital materials derived from the adjacent rocks of Cedar 

 Mountain, and only in minor part of lacustral beds. It is therefore 

 not a typical section. A good section was not obtained anywhere in 

 the region. A general estimate of the thickness in Stewart and lone 

 valleys would place it in the neighborhood of one thousand feet, 

 although it is possible that this may be less than the accumulation in 

 some parts of these valleys. 



It is not considered that the lacustral series is enormously thicker 

 in the middle of Stewart and lone valleys than along the borders. 

 The presence of masses of the pre-lacustral rocks protruding through 

 the lacustral series at considerable distances from the valley borders 

 tends to negative the view of great thickness, unless it is assumed that 

 the valley areas possessed great relief in pre-lacustral time, for which 



6 The Petrographic Designation of Alluvial Fan Formations, Univ. Calif. 

 Publ., Bull. Dept. Geol., vol. 7, pp. 325-334, 1913. 



