P RE-GLACIAL RIVER VALLEYS OF MINNEAPOLIS 455 



show the depth and width of these buried gorges through- 

 out their courses. The lack of data in former years made it 

 impossible to construct such a map with any degree of accuracy. 

 During the last decade, however, much additional data have been 

 made available, especially at critical locahties, through the sinking 

 of wells and the construction of sewer tunnels and ditches and 

 other excavations, so that it has become possible to show in some 

 detail the character of the old drainage system. As will be seen 

 from a study of the topographic map, the limestone which imme- 

 diately underlies the drift over most of the city has been cut into 

 six segments by pre-glacial stream erosion, and had St. Anthony 

 Falls cut its way about one mile farther up the Mississippi to the 

 mouth of Bassett's Creek before its progress was arrested by arti- 

 ficial means,' there would have been seven separate areas of lime- 

 stone instead of six. 



The present river follows the ancient course, which it has par- 

 tially re-excavated, from a point beyond the north city limits to the 

 mouth of Bassett's Creek in the north central part of the city. At 

 this point the river leaves its pre-glacial channel, turns to the east, 

 and flows southeastward through a young narrow gorge to Fort 

 Snelling, at which point it is joined by the Minnesota River which 

 flows into it from the south. As the map shows, the ancient river 

 valley continued southward from the point where Bassett's Creek 

 now has its outlet and flowed in a broad valley with gradually slop- 

 ing banks southward across the region now occupied by the chain 

 of lakes which comprises Lake of the Isles, Lake Calhoun, and Lake 

 Harriet. At Bryn Mawr Meadows a tributary stream joined the 

 river from the northwest, and its buried channel is now the course 

 of Bassett's Creek between Glenwood Lake and Bryn Mawr 

 Meadows. Glenwood Lake also lies within this tributary valley. 

 A second tributary stream joined the main river from the west, just 

 opposite Lake of the Isles. The presence of a buried valley east of 

 this point is suggested by a series of basin-like depressions, one of 

 which is the site of Cedar Lake. The existence of a third tributary 

 valley opposite the south end of Lake Calhoun is indicated by well 



' A protecting apron of timber was built over the rock at the point of fall to pro- 

 tect the rock from further erosion, which threatened to destroy the falls. 



