BT. jonx.] REGION OF m'cOY CREEK. 401 



along the nortbeast border of tliis riilge oeciu\s in wbicb tbe strata bavo 

 been greatly disturbed, probably resulting in faulting or sharp folding, 

 by which the beds on tlie northeast side were suddenly dropped down 

 or greatly pinched, ]\Iore than this was not suggested by the api)ear- 

 auces as seen from a distance. 



With a brief review of the leading stratigraphic and structm'al fea- 

 tures elicited in the course of the examinations detailed in the foregoing 

 sections closes the accoimt of the observations made in this most inter- 

 esting mountain range. The eastern portion of the McCoy Creek sec- 

 tion shows a rather broad and shallow synclinal depression (A), the 

 outskirts of which are based upon a series of red sandstones and varie- 

 gated red and di'ab shales, which are doubtfully regarded as of Triassic 

 age. This depression is the same as tha^ previously observed to the 

 west of Station XXVI and east of Station XXYII, and which appar- 

 ently runs out to the southeast into Salt Eiver Valley. To the north- 

 west, beyond the above-mentioned point west of Station XXVI, it is 

 possible that this fold corresponds to the synclinal trough lying between 

 Stations XXI and XXIV, beyond which it seems to curve round more 

 to the west, where it may pass out into the western border of the north- 

 ern portion of the range, but where it is buried beneath the volcanic 

 flows. The identity of the above-mentioned synclinal depressions is, 

 however, rather suggested than demonstrated ; but when we take into 

 consideration the average prevalent direction of the strike of the strata, 

 it seems so well borne out as hardly to admit of a doubt but that they 

 belong to one and the same trough. 



Some three and a half miles within the debouchure of McCoy Creek 

 the strata rise nj) in a rather narrow fold (B), with steep or vertical dip 

 on the southwest flank, where the dark- weathered conglomeritic sand- 

 stones are seen to arch up toward the crest of the fold in the escarp- 

 ment exx)osures on the south side of the stream at its north bend. This 

 fold is immistakably identical with that in Station XXVII ridge, the 

 axis of which also corresponds to the crest of the lofty massive mount- 

 ain a few miles to the northwest, whose summit dominates the region 

 between McCoy and Pyramid Creeks. Beyond the latter point, how- 

 ever, it is not so clearly traceable. There are uijlifts and westerly inver- 

 sions in the vicinity of Stations XXI and XX, which certainly occiu' in 

 Mne with the i)revaihng strike of the strata between these distant local- 

 ities, but at the latter locality they are so diflerent physically, and more 

 complicated, as to conceal their relations until the structural features 

 were plotted on the topograiihical sheets ; for on McCoy Creek it does 

 not appear that the uplift was so great and the lateral forces so power- 

 ful as to topple the fold over, inverting the strata, such as don bless was 

 the result in the northwest. Yet we find an approach to such a state 

 of things, the western flank showing beds tilted to verticality, though 

 they soon resume gentler inclination, and finallj" sink into a moderately- 

 shallow synclinal trough (C). Southwest of the axis of the latter depres- 

 sion the strata gradually steepen in theii- rise as we pass up the valley 

 until reaching a point 1.} to 2 miles by the stream, but probably Avithin 

 that distance along a line at right angles to the strike, when they 

 abruptly flatten out in a broad-to])i)ed arch, a couple of miles across, as 

 shown at D. The present uplift must represent a displacement of at 

 least several hundred feet, bringing to view a calcareous horizon, which 

 probably belongs to the Jm^assic. The spiclinal on the northeast is 

 mainly filled with sandstones and shales, in regard to the age of which 

 more exphcit data was not obtahied than that they are of Liter date 

 than the Jm-assic limestones, which form the central bauds in the anti- 

 26 GS 



