BT. jonx.] MOUNT CARIBOU. 403 



previously (lescriberl ou the east fork of John Gray's Creek, a few miles 

 to the northwest, while the trend of the folds at the latter locality ren- 

 ders it almost certain that the two sections are structurally, and probably 

 stratigTapliically, identical. Could it have been deternuned by actual 

 examinations wliether the trend of these prominent structural lines in 

 the present quarter bear a little east of their apparent regular course, 

 which they are known to do within still more local limits, the above 

 anticlinal and syncbnal folds might have proved to be actually identical 

 with the folds (x and F of the McCoy Creek section. This interpreta- 

 tion would at once refer the exceedingly variable and complicated struc- 

 tui-al features noticed in the vicinity of Stations XVIII and XIX to the 

 remarkable exhibitions of vertical displacement which are so uinnistak- 

 ably displayed at the upper enti-ance to McCoy Creek Valley, and which 

 are shown at E in the accompanying diagram of the McCoy Creek sec- 

 tion. 



In connection with the sedimentaries in Mount Caribou are associated 

 volcanic phenomena of greatest interest. Scarcely is the ascent of 

 the northeast spiu- along Bilk and Iowa gailches begun, when intrusive 

 ledges of volcanic matter appear ; but it is only on gaining the crest and 

 examining the section exposed in the walls of the little amphitheatre 

 just under Station XXVIII that their true relations were unequivocally 

 disclosed. It would, however, require a much more extended examina- 

 tion than any we were able to make in order to describe in detail the 

 variable character of the erui)tive materials here met with, and which is 

 barely more than hinted in the description of the foregoing section. 

 Besides the regular intruded sheets of volcanic matter, the shales in cer- 

 tain horizons seem to have been permeated with mineral vapors, to which 

 may be attributed the formation of the "mineral pockets" met with in 

 these deposits. The whole mass of the sedimentaries has undergone 

 raetamorphism to greater or less extent, either by direct contact with 

 the intruded sheets or by less direct though probably equally potent in- 

 fluences arising from the same source of volcanic action. But, besides 

 the intrusive matter, there occur exhibitions of eruptive origin on even 

 a grander scale. A short distance fi*om the summit in the northeast 

 face of the mountain there appears a nearly vertical dike-like mass of 

 dark bluish-gray eruptive rock, which has a strike approximately east- 

 west. Passing out along the crest of the western spur of the mountain, 

 the sloping summit is paved with limestone and brittle metamorphosed 

 slate, the latter terminating in a nipple half a mile or so west of the 

 station, where it is associated with a gray sandstone. At the latter 

 l)oint the sedimentaries are cut by an enormous mass of eruptive char- 

 acter, consisting of a dark bluish-gray, hornblendic trachyte, bke that 

 in the before-mentioned dike under the northeast brow of the mouutain, 

 and which presents more the api)earance of an extremely fine, syeuitic 

 rock, in places changing to a scliistose character from the prevalence of 

 mica, which but for the fact of its unmistakable origin would be unhesi- 

 tatingly referred to the metamorphic schistose series. This mass is suc- 

 ceeded on the west by a pinkish-gray, hornblendic trachyte of similar 

 character, occiu-ring in weatliered slabs, and which extends far down 

 along the crest of the steeply descending spur, until its foot merges into 

 the low, rolling sedimentary hills which here liank the mountain, and in 

 whose bared sides exposures of red shales and sandstones rea])pear, in- 

 clining to the southwest. This si)ur forms the southern rim of the great 

 crater-like excavation in the northwest face of the niountain, the distant 

 view of which i>resents so interesting a feature as seen from that direc- 

 tion. The northern spur appears to be made up of sedimentary and 



