st.johx.] GROS VENTRE RANGE. 451 



To the northeast of Station XL VI, in the opposite face of the deep 

 broad gorge in that direction, the strata, Carboniferous, form a low arch. 

 Following along this high ridge, which is apparently the same that 

 forms the north flank of the range along the south side of the mountain 

 course of Gros Yentre Biver, to a point about east-southeast of XL VI, 

 the escarpments defining the deep drainage channels reveal at intervals 

 magnificent sections of the sedimentaries in connection with a remarkably 

 uniform uplift which appears to hold about the same magnitude through- 

 out the extent indicated, as seen from Station XLIV. Along the south 

 or southwest flank of this fold the strata plunge steeply, in places vertical, 

 elsewhere flagging gigantic ridges. But in the opposite slope the same 

 deposits dip much more gently in the direction of the Gros Ventre Val- 

 ley, and appear to be faced with an extensive development of "red 

 beds," whose edges often appear in the crests of the huge ridge, which 

 shows in places the whole Palaeozoic series, even the Archaean nucleus 

 appearing in low outliers in the bottom of the intermontane valley. 



The northwestern terminus of this anticlinal fold, or such as the erosion 

 of Jackson's Basin has determined it to be, apparently lies to the south 

 of the debouchure of the Gros Ventre Biver, where its appearance will 

 be described in connection with the notice of the observations in the 

 vicinity of Station XL VI. In this part of the range the lower interme- 

 diate ridges to the eastward are mainly made up of the Silurian limestones 

 and cpiartzite. The former show the rusty weathered exposures so 

 characteristic of the Quebec Group beds in the Teton Mountains, while 

 the superimposed magnesian limestones are accompanied by overlying 

 red-stained limestones with shaly partings so frequently associated with 

 the exposures of the Xiagara and the inferior member of the Carbonif- 

 erous in the same region. These strata dip gently to the east or north- 

 eastward off the crest of the uplift, whose axis at one point culminates 

 near the present summit of Station XLIV. 



Towards the southeast these beds gently rise, where they appear low 

 on the slope descending from a still more lofty and rugged Archaean 

 peak some five miles about south-southeast of Station XLIV. A very 

 irregular deep saddle connects this x>eak -with XLIV, which bears for 

 a part of the way a covering of Silurian beds dipping quite steeply south 

 or southeastward, in which direction they are followed by the Car- 

 boniferous limestones, and in the extremely broken region still beyond, 

 stretchiug across what has the appearance of a profound narrow valley 

 which here intersects the mountains, an enormous development of pale 

 and deep-red strata occurs, the structural features of which, however, 

 it was impossible satisfactorily to make out. 



On the northeast flank of this high Archaean peak an interesting flexure 

 in the Primordial rusty buff beds is finely displayed, the nucleal rocks 

 showing all the peculiar features of weathering characteristic of the 

 Archaean series. This latter fold is in line with the above peak and 

 Station XLIV, and doubtless pertains to the same general uplift. The 

 Station XLIV uplift differs from that previously mentioned a few miles 

 to the northeast, and with which it is probably more or less parallel, in 

 the less regular distribution of the forces that caused the disturbance, 

 and which, but for the immense erosion which has bared its real char- 

 acter, might be mistaken for so many local quaquaversals or a bulging 

 of the sedimentary beds. While, indeed, a section carried along the 

 saddle from one peak to the other represents a broad synclinal depression 

 filled with sedimentary deposits, a transverse section across the saddle 

 ridge also reveals its anticlinal structure, and at the same time its probable 

 intimate relations to the culminating peaks which mark the sites of the 



