THREE RIVER PEAK. 



23 



West of the eastern summit the edges of the lower beds outcrop, and 

 the Gallatin limestone is exposed in the saddle. On the northeast spur of 

 the peak the Flathead limestones are exposed, the dip being N 30° E., 10°. 



THREE RIVER PEAK. 



Tln-ee River Peak is a sharp point whose position at the head of the 

 Gallatin River and of branches of the Gardiner and Madison rivers makes 

 the name appropriate. The slopes rise abruptly from the head of Indian 

 Creek Valley on the east, while to the north an almost vertical wall rises 

 above the deep blue waters of Gallatin Lake. The peak occurs on the 

 western side of the Indian Creek laccolith, and the beds composing it, like 

 those forming the summit of Antler Peak, consist of Paleozoic strata ranging 

 from the Cambrian limestones to those of the Carboniferous. The sedi- 

 mentary rocks are, however, penetrated by several sheets of intrusive rocks 

 which are much decomposed, but represent phases of the Mount Holmes 

 bysmalith. The following section shows the sequence of rocks exposed 

 on the northern spurs of the peak from Indian Creek Pass to the summit: 



Three River Peak section. 



Crowfoot Num- 

 section. Iter. 



f 26a 



24 





.5 o 

 Ss 



23 



12 



11 



10 



1 9 



8 



r i 



l 6 



21-22 



Limestone, crystalline, gray, fossiliferous; contains crinoid stems 



Limestone, light gray, dense, massive, cherty 



Porphyry, fissile, much decomposed, yellow and purple 



Limestone, light gray 



Porphyry, fissile, decomposed and yellow at base; upper half massive and 



fresher 



Limestone, crystalline, light gray, with granular, weathered surface 



Limestone, brownish gray, weathering a light brown; massively bedded; 



with splintery fracture 



Porphyry, light colored, nearly white, weathering brown, fissile; thoroughly 



decomposed 



Limestone, baked by porphyry 



Porphyry, fissile, yellow and rusty gray, thoroughly decomposed 



Limestone, black and rusty, much baked 



Porphyry, dense, compact, looking like quartzite 



Limestone, thinly bedded, dark and light gray, magnesian 



5 1 



II 



V 15-20 4 Limestones, in a series of beds, not individually noted . 





'iu 



11 





%i 



I 







1 1 13 

 IE J 



1 



Limestone, thinly bedded 



Mottled limestone, matrix light brown, mottled with black; due to aggrega- 

 tion of black grains of matrix 



Gray, blue-gray, brown, and black limestones, with layers of "glauconitic" 

 limestone, the grains black instead of green. Is fossiliferous. Thickly and' 

 thinly bedded', with some yellow argillaceous layers and one conglomerate 

 bed 



Feet. 

 75 

 30 

 15 

 25 



30 

 5 



35 



50' 



. 10 



17 



5 



25 



130 



160 



70- 



40' 



100' 



