IGNEOUS ROCKS OF THE ALGONKIAN SERIES 349 



ture will evaluate the amount by which erosion has reduced altitudes 

 relatively on the several rock types — argillite, limestone, quartzite, and 

 diorite. The determinations may be checked on some surviving areas 

 of ancient relief. When existing profiles have been raised or lowered in 

 accordance with these values, there will result a surface, which, in the 

 writer's judgment, will closely correspond with the peneplain over Gal- 

 ton range. The conclusion involves elements which the eye cannot 

 rightly estimate in the field and for which precise data are not at hand. 

 For this reason the writer is disinclined definitely to place the peneplain 

 relatively to the heights of the Front ranges; but, recognizing the insig- 

 nificant extent of summit areas, or of shoulders that might support 

 modified monadnocks, he thinks it may be located on top of the highest 

 peaks rather than below them. 



On the same ground of inadequate data, the extremely intricate prob- 

 lems of sculpture must be left to the future. The student who may read 

 the record will find it replete with facts of waterwork and icework, and 

 he may discuss evidences of distinct episodes of uplift or of glaciation 

 which the writer has not ventured to interpret. 



Igneous Rocks of the Algonkian Series 

 By George I. Finlay 



GENERAL COMMENT 



Occurrences of igneous rocks in the Front ranges, so far as observed, 

 are limited to the Siyeh formation and a dike in older rocks on Trail 

 creek west of Waterton lake. The drift of the North Fork valley con- 

 tains boulders which represent other rock types. 



The igneous rocks of the Siyeh limestone are two — an intrusive dio- 

 rite and an extrusive diabase. They are described below. The dike 

 on Trail creek is a diabase. 



DIORITE 



On mount Gould, and on mounts Grinnell, Wilbur, and Robertson 

 there is found a band of diorite 60 to 100 feet thick. Near the upper 

 and lower surfaces this intrusive sheet was chilled and is fine-grained. 

 In the center the texture is medium or fine-grained. Several dikes 

 which have acted as conduits for the molten rock are exposed in the 

 region near Swift Current pass. One of these extends across the cirque 



