ST. JOHN.] EEGION OF JOHN GRAy'S LAKE. 359 



or ill a general S. S.W. and K N.E. direction. It vnll further have been 

 observed that the strike of the ledges which compose the moiioclinal 

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

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

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

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

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

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

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

 from the northeast flank of the ridge and abru])tly 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 Eange; yet this relationshij) is 

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

 plain which fills the interval the sedimentaries 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 coiu-se, 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 XVII 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 within 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 How ; but in the mid-vaHey ex- 

 tensive tracts of level alluvial meadow-lands exist, through ^^ iiich 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 Bange 

 considerable areas are covered by Avhite 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 fiUed with meadow-lands, and toward the south boundary of the 

 district it is occupied by a permanent body of shallow water, A^■hich is 

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

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

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

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

 tracts on all sides. Indeed, the greater portion 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, ])erha])S a hundred feet 

 high, Avhich shows in the summit, near the southern end, a rather i)romi- 

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

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



