REPORT OF TEE CHIEF ASTRONOMER 77 



SESSIONAL PAPER No. 25a 



origin in the deposition of land detritus on the sea-floor. A study of all the 

 available facts has, thus, forced the writer to the belief that the huge Siyeh and 

 Altyn formations are chiefly the product of long continued throwing down of 

 calcium and magnesium carbonate from sea-water, from which there was a 

 likewise slow deposition of silicious muddy matter brought from the lands. 

 The molar-tooth structure, of the Siyeh is secondary and was developed after 

 burial. 



Sheppard Formation. 



General Description. — Conformably overlying the Purcell Lava in the 

 Clarke and Lewis ranges is a group of strata which has been named the 

 * Sheppard quartzite ' by Willis. He speaks of it as belonging to a 



' distinctly sandy phase of deposition a quartzite which is 



very roughly estimated to have a thickness of 700 feet. It forms the crest 

 of Lewis range in the vicinity of Mount Cleveland and Sheppard Glacier 

 between Belly river and Flattop mountain [type locality]. It has not been 

 studied in detail but is recognized as a distinct division of the series.'* 



The lithological character of the beds occurring in the Boundary sections 

 and equivalent to the strata at Willis' type locality differs somewhat from the 

 character stated in his brief description. This lack of accordance may possibly 

 be explained through actual differences in the beds as they are encountered 

 at different points along the axis of the Clarke range. It may be noted, how- 

 ever, that the present writer, during a rapid traverse across the Lewis range 

 via the Swift Current Pass, found that there the beds of the Sheppard forma- 

 tion are extremely like those studied in the Boundary belt. The staple rock 

 of the Sheppard is not easy to diagnose in the field. It was only after micro- 

 scopic study that one could be sure of the true nature of the sediment. Its 

 colour, compactness, and general habit are those of an impure, flaggy quartzite. 

 The thin section shows that the rock is largely composed of carbonate (dolom- 

 ite) and that quartz occurs as minute grains rather evenly distributed through 

 the mass of carbonate. The staple rock of the Sheppard is, thus, in the 

 Boundary belt and probably also farther south, a silicious dolomite or dolomitic 

 quartzite. More typical quartzite occurs as a subordinate constituent of the 

 formation, as shown in the following columnar section of the formation where 

 exposed just north of the Boundary monument on the Great Divide: — 



Columnar section of Sheppard formation. 



Top, conformable base of Kintla formation. 

 580 feet. — Thin-bedded, light gray, highly silicious dolomites, weathering buff — a 

 homogeneous member occasionally concretionary; some of the more 

 silicious beds -ipDroximating magnesian quirtzice. 

 20 " Beddish, interbedded quartzite and silicious argillite. 



600 feet. 



Base, conformable top of Purcell Lava. 



*B. Willis, Bull. Geol. Soc. America, Vol. 13, 1902, p. 324. 



