REPORT OF THE CHIEF ASTRONOMER 71 



SESSIONAL PAPER No. 25a 



yellowish leucoxene. The pores of the rock seem to be entirely filled with deep 

 green chlorite. The rock is too greatly altered to afford a useful analysis but 

 it is evidently a common type of basaltic lava. 



Siyeh Formation. 



In Willis' original description of the ' Algonkian ' rocks of the Lewis 

 range, the following concise account of the Siyeh formation occurs : 



' 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. Occasionally it assumes slabby forms and contains argillace- 

 ous layers. It is dark blue or grayish, 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 separated 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 deposition, or to horizontal 

 compression' of the stratum in which the forms occur. Other strata con- 

 sist 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 alternating flatfish 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 bedding planes, and it is possible that the peculiar- 

 ities are due to development of concretions and to breaking up of a super- 

 ficial hard layer on the limestone ooze during deposition of the beds. 

 Walcott has described similar structure as intraformational conglomerates. 



' The Siyeh limestone forms the mass of Mount Siyeh, at the head of 

 Canyon creek, a tributary which enters Swift Current at Altyn from the 

 south. It constitutes the upper part of all the principal summits of Lewis 

 range north of Mount Siyeh, including Mounts Gould, Wilbur, Merritt, 

 and Cleveland. It extends beyond Waterton lake westward into the 

 Livingston [Clarke] range and forms the massive peaks between Waterton 

 and North Fork drainage lines. Above Upper Kintla lake it is sculptured 

 in the splendid heights of Kintla peak and the Boundary mountains.'* 



*B. Willis, Ball. Geol. Soc. America, Vol. 13, 1902, p. 323. 



