402 WEED AND PIRSSON 
covering of well-rounded stream gravel, in part of local origin 
and in part brought from glacial deposits. It is the type so 
common throughout the state south of the glacial boundary. 
North of the mountains the country is covered by the terminal 
moraine of the two continental glaciers. The surface is a rolling, 
broadly undulating plain with rounded, flat-topped ridges and 
low and wide intervening hollows. The larger drift is chiefly 
Laurentian and is mostly buried, except where washed out by 
rains or exposed on wind-blown surfaces. Bowlders over two 
feet in diameter are rarely seen. The quartzite drift of Rocky 
Mountain origin constitutes the bulk of the material and consists 
of smooth-surfaced, well-rounded pebbles and small bowlders of 
red, green, and vari-colored, well-indurated quartzites. Nearing 
the mountains the terminal moraine becomes more accidented, 
and there is a gradual ascent to a point a few miles below St. 
Paul’s Mission, where it ends. 
Cretaceous beds are seen exposed near the foothills, and 
steep, grassy, slopes rise up to the white wall of limestone that 
everywhere encircles the mountains. This limestone wall is per- 
haps the most prominent feature of the mountain mass when it 
is seen from a distance, the huge white scollops into which the 
sharply upturned beds have been cut by erosion being visi- 
ble for fifty miles from the surrounding plains. Above this 
limestone wall dark wooded slopes rise abruptly to the rounded 
summits of the mountains. 
Geological structure—TYhe mountains are formed by a single 
dome-shaped uplift having a nucleal core of crystalline schists, 
and involving Palzozoic limestones and the softer overlying 
Mesozoic beds. This structure has been slightly modified by 
the intrusion of a great laccolithic body of granite porphyry. 
The uplift fades out in the minor puckerings of soft Cretaceous 
beds about the mountain flanks. The strata underlying the sur- 
rounding plains are essentially horizontal. This geological 
structure is shown in the accompanying diagrammatic cross- 
section of the uplift, Fig. 3, p. 412, which shows the relatively low, 
broad character of the folding and the relation of the granite 
