170 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



In both series of analyses the absolute amount of each oxide, except CaO, 

 MgO, and CO.,, varies almost in simple inverse proportion to the quantity of 

 (calcium and magnesium) carbonate which enters into the different rocks. It is to 

 be noted, however, that in the non-carbonate portion of each rock, the iron oxides 

 increase as the content of carbonate increases. The non-carbonate portions 

 have been calculated to 100. The new percentages of the iron oxides in the 

 respective rocks are noted in the following table : — 



Fe,0 3 FeO 



Kitchener, western phase -69 3'04 



Siyeh, Galton series 2-74 1-67 



Siyeh, Lewis series 3-30 2-60 



Creston, western phase 49 1-38 



Creston, eastern phase 243 1-37 



Upper Altyn, Galton series 544 7-00 



Altyn, Lewis series 3-20 1-70 



The fact expressed in the table goes far to explain the much stronger 

 rusty or buff tint of the weathered rock throughout the Galton and Lewis series, 

 as compared with that of the equivalent strata in the Purcell or Summit series. 

 Under weathering conditions the carbonate of the eastern rocks is dissolved 

 out, leaving the more insoluble, ferruginous material in the weathered crust. 

 The pigmentation of the buff-weathering dolomites is, in part, also probably 

 due to the presence of a small amount of the siderite molecule in the carbonate. 



At many horizons the non-dolomitic sediments likewise tend to become 

 more ferruginous in direct proportion to their respective distances from 

 the old shore-line in the west. Thus, the deep-red metargillites and quartzites 

 of the Kintla and Grinnell formations are connected, through the transitional 

 Phillips and Wigwam formations, with the rusty -brown Moyie metargillite 

 and Kitchener quartzite, both of which are much less charged with iron com- 

 pounds. In their respective series, 550 feet of Phillips red beds (Galton series) 

 correspond to the 800 feet of Kintla red beds (Lewis series) ; similarly, 1,200 

 feet of Wigwam red beds (Galton series) correspond to over 1,500 feet of 

 Grinnell red beds (Lewis series). The Kintla and Phillips together form a sub- 

 prism of red rocks which feathers out to nothing somewhere about the medial 

 line of the Purcell range. The Grinnell and Wigwam form a second sub-prism 

 of red rocks which also runs to a feather-edge in the Purcells. The uppermost 

 beds of the Siyeh formation redden strongly as the sections are followed 

 eastward from the Yahk river. Finally, the equivalents of the gray to 

 rusty-gray upper strata of the Creston are dark reddish-brown in the Hefty 

 sandstone of the Galton range and are either deep red shales and sandstones 

 or buff-weathering, impure limestones in the lowermost Appekunny. 



It is clear that the great geosynelinal prism is a very heterogeneous body. 

 It is composed of a large number of formerly horizontal sub-prisms of stratified 

 rock. These are intimately dove-tailed together and some of the sub-prisms 

 have complicated multiple edges. As a ride these edges are not sharp, since 

 the rock of one prism merges gradually into the contemporaneous material 

 of a sub-Drism of a different rock type. 



