200 BULLETIN UNIVERSITY OF MONTANA 



Lichens were probably the first forms of vegetable life to appear. 

 These probably aided in the process of rock disintegration. As lichens 

 apparently secure the greater part of their nourishment from symbiotic 

 algae growing within their tissue they could and did thrive. Their de- 

 caying tissues formed the first vegetable loam which could support the 

 higher forms of life. As other forms of vegetation appeared in succes- 

 sion the soil and rocks were held more firmly in place, making the tearing 

 down process very much slower. 



In later times came the ice age. The whole region was covered with 

 a mantle of ice. How deep the river was is mere speculation. From the 

 country adjacent to the laboratory which has been swept by it the depth 

 was many hundreds of feet. At the lower end of Flathead lake a huge 

 dam 450 feet high was left by the ice. At this time the lake was several 

 hundred feet deeper than at present, and covered much of the northern 

 valley, flooding the land on which the laboratory now stands. 



How many advances and retreats of the ice mass covered the valley 

 must be determined by more extended study, and by one more competent 

 than L Whether the main glacial mass was local or continental must 

 be determined by others. From a careful study of the region I can give 

 only the results as evidenced by glacial action. 



During the glacial period large masses of ice no doubt slid down the 

 steep mountain slopes into the wider ravines and valleys below, in the 

 same manner as ice masses on mountain tops at the present time. These 

 glaciers flowed into one large glacier whose movement was occasioned for 

 the most part by the pressure from behind. The present valley of the 

 Swan river was filled with ice whose movement was northward. At the 

 same time a much larger ice mass vv^as crossing the wide lake valley 

 from the north. I am not able to say whether the ice mass slid over the 

 frozen lake or whether it aided in gouging out a deeper bed. I am in- 

 clined to the former view. 



This will be better understood from a study of the map of the region, 

 Fig. 4. The first ice river had a direction represented by the present bed 

 of Swan river. The second and larger ice mass had a direction across 

 Flathead lake from north to south. At the low end of the Mission range 

 these two forces met. The larger turned the smaller first at a right 

 angle, then back on its course, but on the opposite side of the Mission 

 range. On the ground in the immediate vicinity of this laboratory this 

 meeting took place. It must have been a grand sight could it have been 

 witnessed. 



Also consult Fig. 5, which is a photograph from the summit of Mac- 

 Dougal peak in the Swan range. The Swan river ice flow came down 

 from the left in the picture. The main flow was from the right. They 

 met in the middle foreground. The lower summits immediately in front 

 of the lake toward the observer were ground over by the ice mass. 



On the summits southeast of the Biological Station, which may easily 

 be visited, large boulders, weighing many tons, lie stranded. They are 

 well marked with glacial grooves, and are silent witnesses of the great 

 force which must have been used in their transportation. On some of the 

 summits where the rock strata are undisturbed may be seen deep and 



