PAPERS PRESENTED AT GENERAL SESSIONS 29 



PLANT COMMUNITIES OF GLACIER NATIONAL 

 PARK, MONTANA. 



W. G. Waterman. Northwestern University 



GEOGRAPHY AND GEOLOGY 



Glacier Park is located in the northwest corner of 

 Montana, extending from the east front of the Rockies 

 across the Lewis and Livingston ranges. The east front 

 of the mountains rises abruptly from the Great Plains, 

 as a result of the formation of the great Lewis over- 

 thrust fault which pushed the mountain strata out over 

 the great plains formation in places as far as fifteen 

 miles. This front or escarpment has been trenched by 

 many streams which flow down from the plateau and 

 find their way northeastward through the St. Mary's 

 river to Hudson Bay or through the Milk River into the 

 Missouri. The continental divide runs south along the 

 crests, first of the Livingston and farther south of the 

 Lewis Range, and the waters from the west side of the 

 divide flow eventually into the Pacific Ocean. These 

 streams in their lower valleys have developed narrow 

 flood-plains, but they rapidly become steeper and their 

 head waters are located in mountain ponds and springs 

 on an average not more than 8 or 10 miles west of the 

 plains. The mountain sides are very steep and are 

 covered by slides of gravel occasionally broken by hori- 

 zontal ledges formed by the protruding edges of the 

 strata of which the mountains are composed. These 

 strata dip gently in both directions toward a central val- 

 ley between the two ranges, forming a great syncline. 

 They are generally almost horizontal, though occasion- 

 ally crumpled into many short wavy folds. 



Near the summits of the mountains on protected ledges 

 and in saucer-shaped depressions are located the glaciers 

 from which the park gets its name. They are mostly 

 small and decreasing in size, but they produce charac- 

 teristic ridges of clay and gravel known as moraines, 

 and their melting supplies the streams which cut narrow 

 gorges down the mountain sides. Where two glacial val- 

 leys start opposite each other on the divide, their heads 

 have cut the ridge down and a saddle or pass has been 



