1914] Buwalda: Pleistocene Beds in the Mohave Desert 449 



rests for the most part on the gently sloping alluvial fans of the 

 Cady Mountains. Near Camp Cady the Manix Beds rest against 

 steep rhyolite slopes. It is improbable that the original area and 

 thickness of the Manix Beds have been materially reduced by 

 erosion. 



Physical Characters. — Arenaceous clays and fine argillaceous 

 sands constitute the bulk of the Manix Beds. Both are of light 

 grayish green color. Quartz, feldspar and mica particles are the 

 abundant coarser constituents; the particles are imperfectly 

 rounded. In a part of the clays and sands there occur occasional 

 grains of feldspar and quartz one-eighth to one-quarter inch in 

 diameter, representing the little modified disintegration products 

 of granitic rocks. Of equal persistence with the sand and clay 

 strata are a few thin members which consist entirely of similar 

 partially rounded grains. Such strata are decidedly cross-bedded. 

 Excepting a little gypsum occurring locally as veins in the clays 

 and sands, there is no trace of calcareous or other precipitates 

 so commonly interstratified with Cenozoic lacustral deposits in 

 the Great Basin region. 



The most notable characteristic of the Manix Beds is the strik- 

 ing evenness, persistence, and parallelism of the individual strata. 

 In such areas as that several miles southeast of Manix no irreg- 

 ularity of stratification is apparent in a view showing two to 

 three miles of practically horizontal beds. The individual strata 

 commonly show little lamination. The differences which dis- 

 tinguish different layers are principally those of slight variation 

 in coarseness of materials or in shades of color. (See pi. 23.) 



The upper part of the lake-beds is usually separated from the 

 lower by several feet of relatively coarse material, presumably 

 indicating a short period of contraction or dessication of the 

 lake and fluviatile deposition of coarser, more highly oxidized 

 yellowish material. Except for this interruption the beds appar- 

 ently record a period of continuous deposition. 



Besides the evidence afforded by the remarkably even and 

 persistent bedding, the fine texture, and the green deoxidized con- 

 dition of the sediments, further proof of the lacustral origin of 

 the Manix Beds lies in the abundance at more than one horizon 

 of fresh-water organisms. Fish vertebrae and four species of 



