BT.joiix.] REGION OF STATION XX. 371 



imposed series of red deposits wliich, probably, in part, at least, pertain 

 to a geological epoch as late as the Laramie. The lew data afforded by 

 the fossils in the upper limestones of the precedin<>- section are ample to 

 determine tlieir Jurassic age, and so, also, of tlie lower limestones in the 

 present section ; and although their exact equivalents in the two sec- 

 tions may be left unsettled, they cannot be far removed ; the bed 85, if 

 it is not identical Viith that of the same number in the former section, 

 cannot be far removed from that bed or overlying it in the inverted posi- 

 tion of these strata. At the latter locahty it was observed that the 

 X)lant-bearing sandstones and the associated red shales, which, under 

 any circumstance, would not be referred to a period more remote than 

 the Cretaceous, while they are believed to be not older than the Laramie, 

 l>itch into the mountain-side where they occupy a position api)arently 

 conformable to and underlying well-determined Jurassic horizons. If 

 the appearances above alluded to are correctly interpreted, and there 

 seems to be no other interjiretation admissible, then we liave the other- 

 wise anomalous position of these strata fully explained in their being 

 involved in disturbances which resulted in their upheaval and inversion. 

 There is no evidence of faulting in the strata at this point by which the 

 relative position of the plant-beds might be attributed to a downthrow 

 on the south flank of the uplift. JJence, on the strength of the observed 

 facts and inferences derived from all but as good sources, in reproduc- 

 ing the sections across this part of the range, the structural features 

 are given in accordance with the above-expressed conclusions. 



Assuming the inversion of the strata south of Station XX, it is ap- 

 parent that the arch of the fold has been comidetely denuded in the 

 mountain ridges bordering on Fall Creek Canon. But to the north there 

 are signs, as above mentioned, of the existence of remnants at least of 

 the beds that spanned the great fold. If the uplift represented a dis- 

 placement of hundreds or even a few thousands of feet, the work of 

 erosion has more than half demolished the structure erected by the 

 dynamic agents which uplifted and corrugated the accumulations of ages 

 of deposition on the ancient sea -beds. 



The northwesterly extension of Station XX ridge shows here and there 

 remnants of the peculiar rusty vesicular lava, the disintegration of 

 which has strewn the surface with fragments of obsidian. These vary 

 in color from jet black through various shades of lavender to drab, with 

 spherulite disseminated through their mass. The obsidian appears to 

 have been in concretionary masses, probably imbedded in the lava. At 

 numerous points along this ridge, red shales and even sandstones a]>pear 

 to have been more or less changed by metamorphic action, probably 

 derived from proxiniity'of the volcanic material. The relation of this 

 rock to the sedimentaries was not satisfactorily revealed here ; but it seems 

 most probable that these remnants belonged to an immense flow which 

 spread over the high lands when their surface was more even, or before 

 erosion had fashioned it into its present complicated topographic re- 

 liefs. The deposit here reaches an altitude of about 7,400 feet; and was 

 again met with a few miles to the northwest, where it apparently forms 

 a part, at least, of the volcanic cap of high benches sloping oft" in the 

 direction of Willow Creek. 



About a mile northwest of Station XX, in a corresponding height, a 

 heavy ledge, of brown weathered sandstone appears, dipping west of south 

 at an angle of 35o. Between this point and the station, a similar bro^^^l- 

 ish-red laminated sandstone outcrops in the crest of the ridge beneath 

 the lava, where it dips at an angle of 4~P to the north-northeast. It is 

 associated with red indm^ated shales, and probably holds a stratigraph- 



