MC£3 



CONTENTS, 



Page. 



Letter of transmittal xm 



Outline xv 



Chapter I. — Descriptive geology of the Gallatin Mountains, by J. P. Iddings and W. H. 



Weed 1 



Introduction 1 



The Crags and vicinity 3 



The Crags 3 



Crowfoot section 6 



Mountains south of Panther Creek 9 



South End Hills 10 



Trilobite Point 11 



The Dome 12 



Indian Creek laccolith 13 



Mount Holmes bysmalith 16 



An tier Peak 20 



Three River Peak 23 



Bighorn Pass .., 24 



Crowfoot Ridge and Gallatin Valley 27 



Quadrant Mountain, Bannock Peak, and the valley of the Gallatin River 31 



Bannock Peak 31 



Quadrant Mountain 33 



Little Quadrant Mountain and Fawn Creek Valley 36 



Little Quadrant Mountain , 36 



Fawn Creek Valley 39 



Region north of Gallatin River - 41 



The Fan 45 



Electric Peak 50 



Western flanks of the Gallatin Range 56 



Eastern flank of the Madison Range 57 



Chapter II.— The intrusive rocks of the Gallatin Mountains, Bunsen Peak, and Mount 



Everts, by J. P. Iddings 60 



Indian Creek laccolith 60 



Hornblende-mica-andesite-porphy ry 60 



Mount Holmes bysmalith „ .- 64 



Dacite-porphyry 64 



Bighorn Pass sheet 69 



Kersantite 69 



Gray Mountain mass and connected sheets 73 



Hornblende-miea-andesite- porphyry and andesito 73 



Hornblende-andesite-porphyry and andesite 77 



Ilornblende-pyroxene-andesite-porphyries and andesites 80 



Chemical composition 81 



v 



