634 W. A. JOHNSTON 



but in a body of water which covered not only the Rainy River 

 and Lake of the Woods districts but also occupied Red River valley, 

 and that this was the last great glacial-marginal lake in the region, 

 viz., Lake Agassiz. 



Numerous sections also show that weathering and erosion took 

 place during the interval of erosion before the deposition of Lake 

 Agassiz sediments. This is well shown in sections along the Rainy 

 River from one to three miles below the town of Rainy River. In 

 places, small stream valleys were eroded and later partially or 

 wholly filled with lacustrine deposits. This relation is well seen 

 in the small creek valley which enters the Rainy River three miles 

 below Fort Frances. In one place, on Buffalo Point on the south- 

 west side of Lake of the Woods, thin peaty bands occur in the lower 

 portion of Lake Agassiz deposits. 



The sections exposed on the south shore of Lake of the Woods 

 (Fig. i) afford a demonstration that the water must have risen to 

 a sufficient height to permit of the deposition of the fine lacustrine 

 clays overlying the old wave-cut beach, and it is clear that these 

 waters formed part of Lake Agassiz during a rising stage. There 

 is evidence in the district that the waters rose through a vertical 

 interval of at least 60 feet; for the lake clays are unconformable on 

 the underlying sediments throughout this vertical interval. The 

 highest shore line found in Rainy River district has an altitude of 

 1,200 feet. During the highest stages of the lake, practically the 

 entire district was submerged and the highest shore line, if there 

 had been land high enough to have received it, would have a present 

 altitude of approximately 1,350 feet, as estimated from Upham's 

 determination of the highest beaches in other parts of the basin. 

 It is not certain that the water rose to the level of the highest shore 

 lines recognized in other portions of the basin ; but it seems probable 

 that it rose to the uppermost strong beach (Herman) , because this 

 beach, as already stated, is continuous for a long distance north- 

 ward and is apparently all of one age. It is possible that the 

 Milnor beach which Upham found to be traceable for only a short 

 distance in the southern part of the basin marks a shore line of 

 Early Lake Agassiz, but the extent of this lake or of any of its shore 

 lines is not definitely known. This lake was largely drained 



