1914] Buwalda: Tertiary Mammal Beds in West-Central Nevada 349 



In addition to this folding of the Esmeralda formation, bnt per- 

 haps coincident with it, there occurred a synclinal down-warping of 

 Stewart Valley and lone Valley relative to the surrounding ranges. 

 In numerous localities along the borders of the valleys this has lifted 

 up lacustral beds which lie near the base of the lacustral section to 

 elevations several hundred to a thousand feet or more above beds in 

 the middle of the valleys which are stratigraphically higher in the 

 section. That this down-warping of the valleys and relative uplift 

 of the mountain masses was of the folding rather than of the faulting 

 type is indicated by the patches of lacustral beds reaching up the 

 mountain flanks and by the absence of scarps or fault relations along 

 the flanks of the adjacent ranges. 



Rising and plunging of the synclinal axis of each valley have to 

 a large degree determined the position of the drainage divides in the 

 present valleys and the location of the playa-lake basins of deposition. 



The exact date of the first deformation of the Esmeralda strata 

 has not been determined. It was of course not earlier than the upper- 

 Miocene. The halting of deposition of the lacustral beds was prob- 

 ably occasioned by deformative movements, which would then have 

 occurred about the end of the Miocene. 



It has been shown above that the lacustral strata have been de- 

 formed in two ways : they have been thrown into a series of numerous 

 open anticlines and synelines, and the beds in each valley have besides 

 been thrown into a synclinorium whose limbs extend up the flanks of 

 the adjacent ranges. The last-mentioned deformation of the beds and 

 of the region in general is apparently simple folding on a large scale, 

 each valley being a syncline and each of the mountain ranges, as 

 Cedar Mountain, the Paradise Range, and the Gabbs Valley Range, 

 being relatively uplifted anticlinally. The exact manner in which 

 the minor folds of the lacustral beds in the valleys were produced 

 has been found a matter of difficult explanation. On the one hand, 

 it seems improbable that the relatively rigid rocks underlying the 

 un resistant lacustral beds have been folded into the same small anti- 

 clines and synelines seen in the easily deformed Esmeralda. The 

 alternative is that the yielding lacustral beds acted independently of 

 the rigid underlying rocks and that the minor anticlines and synelines 

 in the softer overlying rocks are not reflected in similar corresponding 

 structures in the rigid rocks beneath them. It is very improbable that, 

 with only such gentle down-warping of the valleys, the adjacent 

 mountain masses have approached each other snfficiently to cause the 



