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GEOGRAPHY: W. M. DAVIS 
THE MISSION RANGE, MONTANA 
By W. M. Davis 
DEPARTMENT OF GEOLOGY AND GEOGRAPHY. HARVARD UNIVERSITY 
Presented to the Academy, November 1 2, 1915 
The Mission Range, one of the smaller members of the Rocky Moun- 
tains in western Montana, beheved to be composed of deformed rocks 
chiefly quartzites, has the appearance of a gently tilted and moderately 
dissected fault block, trending north and south and about 70 miles in 
length. The steeper face, probably representing the battered fault 
scarp, looks to the west. At the low northern end of the range, the 
gently undulating crest emerges from the surrounding plains which 
are about 3000 feet in altitude, and rises slowly southward, reaching a 
height of 9500 feet near its abrupt southern end, thus gaining a local 
relief of 6500 feet. The eastern side of the range is said to slope more 
gently than the western face. The nearly even crest and long eastern 
slope suggest that the mountain mass is an upraised fragment of a 
former worn-down mountain region. 
The western face of the range, which I saw during a Shaler Memorial 
study of another Montana problem in 1913, may be divided as in the 
above figure into three oblique belts by two nearly parallel, south-dip- 
ping planes, about 1000 feet apart. The middle belt includes smoothly 
rounded summits and large- textured, full-bodied, waste-covered spurs, 
between wide-spaced, steep-pitching, apparently consequent ravines of 
normal erosion. All the high-reaching valleys of the southern belt 
expand in cirques of local glaciation at their heads, and continue down- 
wards in narrowing troughs with over steepened walls. These features 
are best developed at the high southern end of the range; there the 
cirques are huge cliff -rimmed cavities, strongly expanded southward; 
the mountain crest is sharpened to Alpine aretes between opposing 
cirque walls; the long troughs, encroaching broadly on the normal 
forms of the rounded spurs, reach the foot of the mountains; and ter- 
minal moraines advance a short distance upon the piedmont plain, some- 
times enclosing a lake in their loop. More than a score of glacial cirques 
and troughs may be counted, but their strength diminishes as the range 
