I>AKES MAHTOMEDl, SlIAKKK, AND AGASSIZ 119 



ing an elevation of 950 feet. It way an incident of the eastward move- 

 ment of the western ice-lobe after it had retreated to the northwest, the 

 hist event of the glacier s occupancy of this part of Minnesota. This re- 

 advance has been studied by Mr Upham and fully descril)ed h}^ him. 

 According; to his interpretation, it was due to an increased ])recipitation 

 over the central and eastern part of the state, by reason of which glaciers 

 were formed again and had a slow movement southeastward, wliere they 

 had been absent for a period of time. This lake had an outlet east- 

 wardly in Washington county through Big Marine lake and Cornelian 

 creek to the Saint Croix river, about 6 miles north of Stillwater. The 

 region of this lake is characterized b}^ a modified condition of the till, 

 which is sometimes itself indistinctly stratified, and by laminated clays 

 due to a more complete washing of the till and the deposition of its finest 

 components in thin sedimentary sheets. As the western ice receded 

 again this lake vanished gradually by drainage toward the west, becom- 

 ing absorbed b}^ a tumultuous flood of gravel-and-sand laden water which 

 passed southwestwardly across Chisago and Anoka counties at a level 

 not much below that of the lake itself. 



r 



10. Lake Shafer 



The eastern part of Chisago county, as far westward as Center City, 

 shows similar indications of a body of standing water at a date nearly 

 cotemporary with that of lake Mahtomedi, the surface of which was 

 about 975 feet above the sea. It appears that the Saint Croix river was 

 obstructed by the last movement of the toe of the western ice-lobe, below 

 Franconia, and was set back in form of a lake whose outlet was in Wis- 

 consin and has not been discovered. It must have been about the eastern 

 border of the ice. 



11. Lake Agassiz 



The largest of the glacial lakes in which Minnesota has any record is 

 that named and investigated by Mr Upham. Beginning in Minnesota 

 he followed this investigation into Dakota and then into Canada.* Its 

 outlet, which was at 1,050 feet above the sea, and its location and out- 

 line are shown on the accompanying map, plate 12. 



Although there may be some variations in the details and sequence of 

 the parts of this great lake, rendered necessary by future researches in 

 the northern part of Minnesota, the lake itself as a whole stands out 

 boldly in its general features, and its effect upon the state of Minnesota 

 is very pronounced and important. It is one of the most marked illus- 



* His final and full report is published as Monograph xxv of the United States Geologicai Survey. 

 Tliis is so well known that no description is called for here. 



