PRE-GLACIAL RIVER VALLEYS OF MINNEAPOLIS 447 



valleys should be a controlling factor in the choice of types of foun- 

 dations for large buildings or other structures erected within the zone. 



The data used in constructing the map and sections have been 

 obtained from many sources, but chiefly from records of excavations 

 for sewers and water mains and from hundreds of well records sup- 

 plied by the well drillers operating in the vicinity of Minneapolis. 

 The surface topography is partly taken from the topographic maps 

 of the United States Geological Survey covering the region around 

 Minneapolis and St. Paul, and partly compiled from elevations 

 supplied by the city engineer, and from field work done in the spring 

 of 1914. 



The writer desires to express his thanks to all those who have 

 given assistance in gathering data for this paper. Special acknowl- 

 edgment is made to City Engineer F. W. Cappelen, Dr. F. W. 

 Sardeson, and to the engineers in the Sewer and Water departments 

 of the City Engineer's ofl&ce; to Mr. A. C. Godward, engineer for 

 the Minneapolis Board of Park Commissioners; Mr. James G. 

 Houghton, city building inspector; Mr. J. F. McCarthy, Mr. E. F. 

 McCarthy, the S. Swenson Artesian Well Co., and Mr. Max Renner. 



II. ROCK FORMATIONS BENEATH THE DRIFT 



The rock formations existing in the vicinity of Minneapolis, with 

 the relative position, thickness, and characteristics of each, are 

 shown in Table I. 



Only four of the formations given in the table may constitute 

 the rock surface immediately beneath the glacial drift in Minne- 

 apolis. These are (i) the Decorah shale; (2) Platte ville limestone; 

 (3) St. Peter sandstone; and (4) Oneota dolomite. The existence 

 of the latter in direct contact with the drift has been determined 

 at only two or three localities within the city limits, where deep 

 wells have penetrated the drift. The localities have been found to 

 lie over the deepest part of the main buried river channel, as shown 

 by the deep well records. Therefore it seems probable that the 

 pre-glacial Mississippi had cut entirely through the overlying for- 

 mations and flowed upon a rock bed of Oneota dolomite from a 

 point near the mouth of Bassett Creek in North Minneapolis south- 

 ward to the city limits and beyond. 



