2 GEORGE V. SESSIONAL PAPER No. 25a A. 191& 



CHAPTER VI. 



STRATIGRAPHY AND STKUCTUKE OF THE PURCELL MOUNTAIN 



SYSTEM. 



PUECELL SEEIES. 



As one leaves the Rocky Mountain system and crosses the wide master 

 trench to study the composition of the Purcell system along the Eorty-ninth 

 Parallel, he enters a much more difficult field. Between Gateway and Porthill 

 the mountains seldom rise above tree-line and the forest cap is, throughout 

 the stretch, of unusual density and continuity. Notwithstanding the steepness 

 of the mountain slopes the timber generally stands thick upon them. Beneath 

 the trees a heavy growth of brush and generally, a discouragingly thick layer 

 of moss and humus, form an impenetrable cover over most of the bed-rock on 

 the Boundary belt. During many traverses made during the season of 1904 

 outcrops absolutely failed for a mile, or even for several miles, at a time. 

 Eield work was further rendered unsatisfactory during that extraordinarily 

 dry season on account of the thick smoke which hung over the mountains. For 1 

 one period of seven weeks the smoke was dense enough to interfere seriously 

 with the work of discovering outcrops. 



In the Purcells the stratigraphic conclusions were rendered all the more 

 delicate because of the remarkable uniformity of the sedimentary formations. 

 It was found that much the greater part of the belt is underlain by the strati- 

 graphic equivalent of the Galton and Lewis series. This equivalent has been 

 named the Purcell series. Very seldom is there represented among its members 

 anything like the lively contrasts existing, for example, between the Kintla 

 and Sheppard formations, between the. Siyeh and Grinnell, between the Appe- 

 kunny and Altyn, or between the respective pairs of formations in the Galton 

 series. For thousands of feet together the strata of the Purcell series exhibit 

 a homogeneity that is bound to excite wonder in the mind of the geologist. 

 In the Moyie and Yahk ranges not a single stratum of marked individuality 

 has been discovered which is proved to persist throughout the ranges. In none 

 of the three ranges has any formation yielded fossils. This failure of well 

 defined horizon-markers in a region of considerable structural complexity is, 

 perhaps, the greatest of the difficulties that confront the geologist in the 

 Purcells. 



For these reasons the writer has not felt justified in attempting to des- 

 cribe the Purcell series in the detail which is warranted in the case of the 

 formations composing the Galton or Lewis series. It has seemed safer to 

 express the stratigraphy of the Purcell mountains in terms of three very thick, 



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