GEOGRAPHY: W. M. DAVIS 
627 
crest lowers northward, and the northernmost cirques are of small dimen- 
sions, faintly developed, and reach only a few hundred feet down from 
the valley heads. The limiting plane which touches the lower end of 
the troughs rises slowly northward from the base of the range at the 
southern end and reaches the crest of the range north of mid-length. 
The lower northern belt of the range shows innumerable bare crags, 
knobs, cliffs and ledges of small texture, due to scouring and plucking 
by the terminal portion of a broad and overwhelming glacier of Canadian 
orig'n. The limiting plane, marking the height of the invading glacier, 
touches the range crest about a quarter length from its low northern 
end and descends to the range base south of mid-length. The northern 
quarter of the range, lying entirely beneath this limiting plane, exhibits 
glaciated forms in a minutely irregular crest and a disorderly slope of 
scoured and plucked hills and hollows, all of less and less height north- 
ward, until the last visible knobs, deeply scored and channeled and more 
or less detached from one another, rise only 100 feet or so above the 
surrounding intermont plain of glacial gravels and silts, diversified by 
low morainic hills, which presumably conceals a farther northward 
extension of the range crest. The second quarter of the range shows 
similar small-textured forms up to the limiting plane, but above it the 
mountain crest and slope retain the simpler, large-textured forms of 
normal erosion, until, near mid-length, the valley heads begin to show 
the cirques of the high southern belt. Through this second quarter 
each normal valley is barred by a niorainic embankment on the line of 
the limiting plane, and below the plane each spur is imperfectly trun- 
cated in a bold and rugged slope which presents a tumult of rocky cliffs 
and ledges, descending abruptly and without well-defined valley reen- 
trants to the waters of Flathead Lake. The apex height of the rugged 
spur facets and the altitude of the somewhat lower morainic embank- 
ments decrease slowly and systematically southward; the facets become 
smaller and less continuous with one another; the embankments become 
longer, larger, and more nearly continuous, until they curve away from 
the range base and form a noble terminal moraine, 400 or 500 feet in 
height and a mile or more wide, which swings westward across the inter- 
mont depression and separates Flathead Lake on its northern concave 
side from a broad till plain of earlier glaciation on its southern convex 
side. 
It is to the long and gradual southward rise of the mountain mass 
that the Mission Range owes the clear separation of features due to local 
glacial sculpture in the high southern belt from those due to general 
glacial sculpture in the low northern belt, by the obHque middle belt 
