6 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. 



separated from it by a fault trending a little west of north. This fault 

 crosses the southern end of Crowfoot Ridge, about a mile west of the 

 summit of Three River Peak, and passes southward along the west base of 

 the mountains, between Indian and Maple creeks, disappearing beneath the 

 more recent rhyolitic lavas. The eastern area embraces the most promi- 

 nent peaks of the southern portion of the Gallatin Mountains, including' 

 Mount Holmes and the bare porphyry peaks around the head of Indian 

 Creek, besides Trilobite Point, The Dome, Antler Peak, and Three River 

 Peak, peaks that are directly connected with the mountains north of Panther 

 Creek. 



CROWFOOT SECTION. 



Before taking up the description of these mountains, involving sedi- 

 mentary rocks, it will be best to give an account of the stratigraphic series. 

 A very carefully measured section was made of the Paleozoic strata exposed 

 on a northern lateral spur of Crowfoot Ridge. This high mountain ridge 

 shows the entire sequence of the Paleozoic sediments of the region, from the 

 crystalline schists to the top of the Carboniferous, exposed in an unbroken 

 succession of apparently conformable beds dipping at an angle of 30° N. 

 The general form and profile of the ridge is shown in PL II, which gives a 

 view of the ridge from the east. The illustration shows the bluffs formed by 

 the harder beds of the series, rising above the slopes into which the shales 

 and thinly bedded strata have weathered down. Two lines of cliffs, formed 

 by the mottled limestone, No. 14 of the section, and the Jefferson limestone, 

 No. 19, are seen in the view. These horizons form characteristic cliffs 

 throughout the range, and are an important aid in reading the structure of 

 the mountains. The section of the sedimentary rocks made at this place 

 has served as a basis of comparison for all the other sections of the Paleozoic 

 rocks made in the Gallatin Range. The beds are well exposed, the crest of 

 the ridge being bare of soil or vegetation and the trend of the ridge being 

 very nearly at right angles to the strike of the strata. 



