ST.J0H2J.] EEGION OF JOHN GEAY's LAKE. 359 



or in a general S. S.TV. and 1ST. X.E. direction. It will farther have been 

 observed that the strike of the ledges which compose the nionoclinal 

 crest of this part of the ridge trends round from a north of east to south 

 of east direction in crossing from the northeast to the southwest side of 

 the ridge, and exhibiting almost the exact counterpart of the condition 

 of things found in the southeastern portion of the Day's Lake ridge. 

 This structure is further indicated by the massing of a heavy series of 

 superimposed red and drab deposits, which make up the bulk of the 

 southern portion of the ridge. Above the pass, a short spur jutting 

 from the northeast flank of the ridge and abruptly terminating in the 

 valley, exhibits a heavy series of dark and chocolate-colored shales and 

 rusty sandstone ledges, which incline at a steep angle toward the main 

 ridge. The latter deposits apparently constitute a large portion of the 

 southwestern extremity of the ridge, and they are supposed to pertain 

 to the Jura-Trias series of the region. 



The geological, as also the topographic, relations of this ridge are 

 apparently intimate with the Blackfoot Range ; yet this relationship is 

 more a matter of inference than actual demonstration. In the basaltic 

 plain which fills the interval the sedhnentaries are, of course, concealed 

 from view, and it may be that both of the latter ridges mentioned above 

 are the result of locally-manifested disturbing causes by which the strata 

 over narrow elliptical areas were bulged up into abrupt anticlinal folds, 

 and probably faulted along parts of their course, as seems to be the 

 case in the northeast side of Station XXIX fold. Yet, while isolated are 

 as of local disturbance may, and doubtless do, exist, as, for example, the 

 Station XYII uplift, this basin region as a whole is doubtless intimately 

 related to the border areas where the most complicated foldings and 

 faulting are prevalent ; and the present isolation of the basin ridges, 

 as also that of the more extensive border mountain belts, is due to sub- 

 sequent erosion. 



That portion of the upper basin of the Blackfoot lying withm our ter- 

 ritory forms a level plain, into which low benches of basalt extend from 

 the basaltic plateaus and neighboring mountain ridges. The whole area 

 is doubtless based upon the great lava flow ; but in the mid- valley ex- 

 tensive tracts of level alluvial meadow-lands exist, through which the 

 stream sluggishly winds between muddy reed- and grass-grown banks, 

 resembling much a tide- water channel. In the adjacent acclivities of 

 Station XXIX ridge and the low divide south of the Blackfoot Range 

 considerable areas are covered by white calcareous tufa, deposits made 

 by springs that issue from the limestone ridges. 



John Gray's Creek opens into a wide, flat basin at its head, which is 

 largely filled with meadow-lands, and toward the south boundary of the 

 district it is occupied by a permanent body of shallow water, which is 

 known as John Gray's Lake. These alluvial lands, consisting of a deep 

 fine brown sod, are exceedingly fertile wherever water is carried upon 

 them. Early in the season the influx of surface drainage greatly extends 

 the ordinary and obscurely-defined limits of the lake, flooding extensive 

 tracts on all sides. Indeed, the greater j>ortion of the lake is merely a 

 marsh, which is being gradually reclaimed by the deposition of fine 

 sediments washed from the bordering uplands and the materials con- 

 tributed by the decay of the dense growths of reeds, grasses, and moss 

 which flourish in the oozy soil. 



In the midst of the lake rises a low island, perhaps a hundred feet 

 high, which shows in the summit, near the southern end, a rather promi- 

 nent ledge of rusty-weathered rock, dipping, at a gentle angle of inclina- 

 tion, westerly or southwest, in which direction the elevation also declines. 



