318 B. WILLIS — LEWIS AND LIVINGSTON RANGES, MONTANA 



In the upper part of the Siyeh limestone there are also large concre- 

 tionary masses which are irregularlj r cylindrical in form, with major axes 

 at right angles to the bedding of the rocks, and which attain the dimen- 

 sions of a keg, and even of a small barrel. Walcott states that these forms 

 are similar to those found in the pre-Cambrian rocks north of Helena, 

 Montana, but as yet they have yielded no evidence of organic origin. 

 "Sir William Dawson considered that they represented a very simple 

 form allied to Stromatopera.' 1 



In the British Boundary Commission report* Dr George M. Dawson 

 describes these ancient rocks under the caption " Review of the Section,'' 

 as follows : f 



" The total thickness of the beds seen in this part of the Rocky mountains must 

 be about 4,500 feet, though this can only be regarded as an approximation, as, 

 owing to the short time at my disposal, few of the beds were actually measured. 

 The entire series, arranged as a continuous section in descending order, is as fol- 

 lows : 

 H. Fawn-colored flaggy beds, seen only at a distance, but probably composed of 



magnesian sandstones and limestones. 100 feet. 

 G (Kintla formation). Beds characterized by a predominant red color and chiefly 

 red sandstone, but including some thin, grayish beds, and magnesian sand- 

 stones, the whole generally thin-bedded, though sometimes rather massive. 

 Ripple marks, &c. Weathers to a steep rocky talus where exposed in the 

 mountain sides, and passes gradually down into the next series. 300 feet. 

 F (Sheppard quartzite). Fawn-colored flaggy beds of magnesian sandstone and 

 limestone. Some red sandstones occur throughout, but are especially abun- 

 dant toward the top. Apparently a continuation upward of the limestone 

 D, and only separated from it by the trap overflow. 200 feet. 

 E Amygdaloidal trap ; dark colored and hard. 50 to 100 feet. 

 D (Siyeh limestone). Compact bluish limestone, somewhat magnesian, and weath- 

 ering brownish. This forms some of the boldest crags and peaks of the 

 mountains, and apparently rests unconformably on Series C. 1,000 feet. 

 C (Grhmell and Appekunny formations). Sandstones, quartzites, and slaty rocks, 

 of various tints, but chiefly reddish and greenish gray ; the individual beds 

 seldom of great thickness, and the color and texture of approximate beds 

 rapidly alternating. In this series occurs a band of bright red rocks, of in- 

 constant thickness ; also two or more zones of coarse magnesian grit. 2,000 

 feet or more. 

 B (Uppermost bed of Altyn limestone). Limestone, pale gray, cherty, and highly 

 magnesian; hard, much altered, and weathering white. It includes at least 

 one band of coarse magnesian grit like that found in the last series, which 

 weathers brown. 200 feet. 

 A (Altyn limestone, upper part). Impure dolomite and fine dolomitic quartzites ; 

 dark purplish and gray, but weathering bright brown of various shades. 700 

 feet or more." 



* George M.Dawson: British Boundary Commission Report on the Geology and Resources of 

 the Region in the Vicinity of the Forty-ninth Parallel, 1875, pp. 67, 68, and Canada Geological Sur- 

 vey Report, 1885, p. 39 B et seq. 



f The names used in this report are inserted in brackets after the letter by which Dawson des- 

 ignated the corresponding beds. 



