CORRELATION 321 



of alternating, flaggy, magnesian sandstones and red sandstones and shales 2,000 

 feet in thickness (p. 60 B). In connection with the red beds, ripple-marked sur- 

 faces, mud cracks, and impressions of salt crystals occur, the whole indicating, as 

 the conditions of deposition of the rocks, those of a basiu cut off from the main 

 ocean. 



" With the single doubtful exception of certain red beds, seen from a distance, 

 near the summit of the White Man's pass (p. 115 B), these Triassic rocks are 

 entirely confined to the district south of the Crow Nest pass, and, as elsewhere 

 more fully shown, we fiud here probably the northern limit of a great Triassic 

 mediterranean sea, which extended far to the southward in the western part of 

 the present continental area." 



Altyn limestone. — The lowest member seen of the Algonkian strata is a 

 limestone. Its unweathered surfaces are dark grayish blue, and in lith- 

 ologic aspect it closely resembles Cambro-Silurian dolomites of the Ap- 

 palachian region and the massive limestone of the Eo-Carboniferous. It 

 is silicious, but there are no visible quartz grains or other evidences of 

 marked mechanical sedimentation. Its stratification is often obscure, 

 partly on account of its massive character and even more because of very 

 decided deformation, which has resulted in faulting and crushing. Its 

 thickness is undeterminable, but probably not less than 800 feet. Suc- 

 ceeding this basal member and included with it in the Altyn formation 

 are limestones which differ chiefly in that they contain more earthy sedi- 

 ment and are very thinly bedded. In consequence of the ferruginous 

 clay contained, they are decidedly yellow, brown, and terra-cotta in color. 

 They are sometimes separated from the underlying massive limestone by 

 a plane, above which they lie flat, while the mass below is greatly dis- 

 turbed (see figure 5, page 334). The effect strongly suggests an uncon- 

 formable relation between the two, but this is not believed to have been 

 the original condition of deposition as they were seen in conformity, 

 where not traversed by thrust faults. The thickness of the thin-bedded 

 upper member of the Altyn limestone is approximately 600 feet. 



The Altyn limestone occurs typically in the cliffs of Appekunny moun- 

 tain, between 6,000 and 7,400 feet above sea, due north of Altyn, in Swift 

 Current valley (figure 2, plate 47). The westward dip carries the base 

 down to about 4,800 feet west of Altyn, where it forms the ledge over 

 which Swift Current falls at the outlet of McDermott lake. Northward 

 and eastward from this locality the limestone forms the cliffs that sur- 

 round Appekunny, constitutes the mass of Yellow mountain, the north- 

 ern slopes of mount Robertson, and the ridge between Kennedy creek 

 and Belly river, ending in the tower-like peak of Chief mountain. Be- 

 yond the forks of Belly river it was traced northwest into Canada and 

 to the narrows of Waterton lake, whence the outcrop trends northward 



XLVIII— Bull. Geol. Soc. Am., Vol. 13, 1901 



