REPORT OF THE CHIEF ASTRONOMER 49 



SESSIONAL PAPER No. 25a 



not far from an Upper Cambrian horizon, and the oldest exposed bed being 

 located well above the base of the Belt terrane. The Summit series includes 

 the entire Belt terrane and a vast thickness of conformably overlying strata 

 which may represent the whole Paleozoic succession up to and including the 

 Silurian. Overlying the Summit series, apparently conformably, is a very 

 thick and massive limestone which is probably Carboniferous but may, in its 

 lower part, belong to the Devonian. In other words, it seems possible that the 

 complete gecsynclinal prism is represented in the exposures of the Boundary 

 belt where it passes through the southern Selkirks. The name ' Summit series ' 

 refers only to the unfossiliferous formation making up the lower and greater 

 part of the prism in this mountain system. 



LEWIS SERIES. 



The writer has carefully studied the Lewis series only within the limits 

 of the Clarke range. Since the Commission map extends but a mile or two 

 to the eastward of the summit monument, a close mapping of the different 

 formations between that monument and Waterton lake was not feasible. In 

 this stretch of fifteen miles the field work was confined to the measurement o£ 

 a few sections. These, however, occurred in areas of unusually complete rock- 

 exposure and much light on the composition of the lower one-third of the series 

 was derived from their examination. In the Lewis range the writer had no 

 opportunity for close work and his experience there was limited to rapid 

 traverses from Waterton lake to Chief mountain and thence, by way of Altyn 

 and the Swift Current Pass, to Belton, Montana. 



Limited as that opportunity was, it sufficed to corroborate the belief — 

 already reached after reading Willis' paper on the ' Lewis and Livingston 

 Ranges ' — that the stratified sequence in the Lewis range is essentially identical 

 with that in the Clarke range. It will, in fact, appear in the following account 

 that the columnar section constructed by the writer from data obtained wholly 

 within the Clarke range, matches well, member for member, with Willis' 

 columnar section derived almost entirely from observations in the Lewis range. 

 Partly in order to emphasize this identity the name ' Lewis serie:» ' has been 

 selected to cover the whole group of strata in the Clarke range — the group now 

 to be described. (See Plate 7.) 



Beginning at the top the formations included in the Lewis series have 

 been listed in the order of the following table : 



Formation. Thickness in feet- Dominant rocks . 



Top, erosion surface. 



Kintla 860+ Argillite. 



Sheppard 600 Silicious dolomite. 



Purcell Lava 260 Altered basalt. 



Siyeh. 4,100 Magnesian limestone and metargillite. 



Grinnell 1,600 Metargillite. 



Appekunny 2,600 Metargillite. 



Altyn 3,500 Silicious dolomite. 



Waterton 200+ Silicious dolomite. 



13,720 



Base concealed. 

 25a— 4 



