THE GALLATIN MOUNTAINS. 9 



MOUNTAINS SOUTH OF PANTHER CREEK. 



The geological structure of the mountains east of the fault already 

 mentioned as crossing Crowfoot Ridge is somewhat complicated by the 

 presence of large bodies of igneous rock that have been forced between, 

 and also across, the sedimentary strata. The exact position of these 

 eruptive masses will appear from the description and map (PL X). In 

 general, the stratified rocks form a flat arch, the central portion of which is 

 nearly horizontal, and beneath which the crystalline schists are exposed 

 along the east base of the mountain escarpment for a distance of 4 miles. 

 The strata immediately overlying these schists at the northern end dip at a 

 low angle, 5°, toward the northeast, and at the southern end they dip about 

 3° toward the southwest. This is the simple structure of the eastern portion 

 of the area along a line through Antler Peak, The Dome, Trilobite Peak, 

 and the hills south of Winter Creek,, which is shown in the geological cross 

 section, PI. Ill, fig. 1. 



The igneous magma which was intruded into the shaly layers of the 

 Flathead formation and was afterwards consolidated as the Indian Creek 

 laccolith, was forced upward from some source at the north, uplifting the 

 strata southward and wedging them apart, and being itself separated into 

 two sheets by a thin, wedge-shaped layer of limestone. The sheets, which 

 are nearly horizontal for a considerable distance, become thinner southward 

 and have only a slight thickness where last exposed in this direction. In the 

 ridge north of Indian Creek the sedimentary rocks overlying the intruded 

 body arch over it from east to west in a pronounced manner, which is shown 

 in cross section in PI. Ill, fig. 2, and which will be described later on. 



Subsequent to the intrusion of this double sheet of igneous rock, there 

 was another outbreak of molten magma of a slightly different character, 

 which was forced upward directly through the rocks just described. The 

 manner of its intrusion is shown by the nature of the contacts between 

 the second eruptive mass and the surrounding rocks. This body forms 

 a great mass, whose present exposure is 3 miles long and 2 miles wide, 

 embracing the six white peaks surrounding the head of Indian Creek, of 

 which Mount Holmes is the most conspicuous. With this preliminary 

 sketch before us, it is possible to proceed to a more detailed description of 

 the geology of this portion of the country. 



