GRINNELL ARGILLITE AND SIYEH LIMESTONE 323 



dipping under the crest of the range at the heads of the great amphi- 

 theaters tributary to Swift Current valley. About the sources of the 

 Kennedy creeks it forms the ridge which divides them from Belly river. 

 Mount Kobertson is a characteristic pyramidal summit composed of 

 these red argillites. The formation occurs in its proper stratigraphic 

 position between the forks of Belly river and west of that stream in the 

 Mount Wilson range of the Canadian geologists, the northernmost ex- 

 tremity of the Lewis range ; and it dips westward under the valley of 

 Little Kootna creek and Waterton lake. On the western side of Living- 

 ston range the Grinnell argillite was recognized as a more silicious, less 

 conspicuously reel or shaly division of the system, occurring about 

 upper Kintla lake. 



Siyeh limestone. — Next above the Grinnell argillite is a conspicuous 

 formation, the Siyeh limestone, which rests upon the red shales with a 

 sharp plane of distinction, but apparently conformably. The Siyeh is 

 in general an exceedingly massive limestone, heavily bedded in courses 

 2 to 6 feet thick like masonry (see plate 49). Occasionally it assumes 

 slabby forms and contains argillaceous layers. It is dark blue or gray- 

 ish, weathering buff, and is so jointed as to develop large rectangular 

 blocks and cliffs of extraordinary height and steepness. Its thickness, 

 as determined in the nearly vertical cliff of mount Siyeh, is about 4,000 

 feet. 



This limestone offers certain phases of internal structure which may 

 be interpreted as results of conditions of sedimentation or as effects of 

 much later deformation. Some layers exhibit calcareous parts sepa- 

 rated by thin argillaceous bands, which wind up and down across the 

 general bedding and along it in a manner suggestive of the architectural 

 ornament known as a fret. It is conceived that the effect might be due 

 to concretionary growths in the limestone, either during or after deposi- 

 tion, or to horizontal compression of the stratum in which the forms 

 occur. Other strata consist of fragments of calcareous rock from minute 

 bits up to a few inches in diameter, but always thin, constituting a 

 breccia in a crystalline limy cement. Again, other strata consist of alter- 

 nating flattish masses of calcareous and ferruginous composition, which 

 rest one upon another like cards inclined at angles of 30 to 45 degrees 

 to the major bedding. At times the lamination is so minute as to yield 

 a kind of limestone schist. These internal structures suggest much 

 compression, but the apparent effects are limited by undisturbed bed- 

 ding planes, and it is possible that the peculiarities are due to develop- 

 ment of concretions and to breaking up of a superficial hard layer on 

 the limestone ooze during deposition of the beds. Walcott has de- 

 scribed similar structures as intrafonnational conglomerates. 



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