RHYTHMIC UPLIFTS A^D STAGES OF REST. 225 



15 to 20 feet below its preceding level. Each of these beaches records a 

 comparatively long- pavLse in an uplifting of the land adjoining the mouth 

 and outlet of Lake Agassiz, which was periodically renewed during brief 

 stages of somewhat rapid increase of elevation at no less than five times 

 while Lake Agassiz outflowed southward. The regularity or rhythm in the 

 sequence of these beaches, and their division by nearly equal vertical inter- 

 vals, were doubtless produced by rhythmic uplifts, alternating with longer 

 stages of nearly complete rest. 



In total the rise of the country about Lake Traverse appears not to 

 have exceeded 90 feet dm-ing the time of existence of the River Warren, 

 and probably it was less. This river is not known to have formed alluvial 

 deposits along its course, building up its bed, but instead was apparently 

 cutting down its channel throughout the whole extent of the yalley now 

 occupied by Lakes Traverse and Big Stone and the Minnesota River, finally 

 flowing at Belle Plaine, in the lower part of the Minnesota Valley, proba- 

 bly 150 feet below the present river and 140 feet below low water in the 

 Mississippi at St. Paul.' A considerable shai-e of the total erosion of 90 

 feet from the Herman to the McCauleyville beach is therefore probably 

 attributable to the descending slope and ordinary downward cutting of the 

 River Warren, independent of its stages of faster rate when the southern 

 part of the basin was being elevated. While these five slight uplifts, prob- 

 ably together not exceeding 90 feet and perhaps no more than 75 or 50 

 feet, took place at the south, a much larger number of elevatory move- 

 ments, mostly of similarly small amount, to be presently discussed, raised 

 the northern part of the lake basin 200 to 300 feet or more, their amount 

 becoming greater from south to north. The little depths that the River 

 Warren eroded dm-ing the several stationary stages of the southern end of 

 the lake basin harmonize well with the small volume of the beach deposits 

 and with the scanty amount of cliff-cutting and other wave action on the 

 shores, all attesting the brevity of the time required for the work done. 



' "The Minnesota Valley in the Ice age," Proc, A. A. A. S., Vol. XXXII, for 1883, pp. 227-231. 

 MON XXV 15 



