184 W. UPHAM — MODIFIED DRIFT IN SAINT PAUL. 



of this area remains in its former condition of fields, pastures, and woods, 

 while the other half is occupied by the broadly extended city * 



The Mississippi river, where it begins to form the western boundary of 

 Saint Paul, has an elevation, in its lowest and highest stages, of about 

 705 and 720 feet ; four miles southward, at Fort Snelling and the mouth 

 of the Minnesota river, its elevation is 688 to 710 feet; six miles thence 

 northeast, at the union depot, 683 to 702 feet ; and about five miles 

 thence southeast, where it leaves the city limits, about 680 to 700 feet. 

 The low-water stage of the river has thus a descent of 25 feet within and 

 adj oining this city. 



Northward from Fort Snelling the Mississippi occupies a postglacial 

 gorge about a fifth of a mile wide between the crests of its bluffs, which 

 are about 100 feet above the river, or 800 feet above the sea. The Minne- 

 sota river and the Mississippi river below the confluence of that stream, 

 with their bottomlands, occupy a valley enclosed by rock bluffs from a 

 half mile to two miles apart. Along the northwest side of the Missis- 

 sippi from Fort Snelling to the capitol, a distance of six miles, the 

 Trenton limestone, which forms the crest of the inner valley thus de- 

 scribed, reaches back as a nearly level terrace from a quarter of a mile 

 to one mile wide, at the height of 790 to about 800 feet above the sea, 

 or a little more than 100 feet above the river. Very scanty deposits of 

 glacial drift, or more generally of modified drift, remain on this rock 

 terrace, their thickness varying from a few inches to a few feet. 



From the river and its bottomlands, and from this terrace, the surface 

 of the country ascends, by steep or by moderate slopes, to a general ele- 

 vation of 900 to 950 feet above the sea. The greatest altitudes attained 

 within the limits of the city are about 1,060 feet near its northeast 

 corner; about 1,020 feet near its northwest corner, close to the State 

 Farm and Agricultural College ; and about 1,025 feet at a distance of 

 one and a half miles north-northeast of Fort Snelling. 



The larger part of the city has a moderately undulating .or a knolly 

 and hilly surface of glacial and modified drift, between 850 and 950 feet. 

 Numerous plateaus of modified drift, gravel and sand, however, which 

 are especially described in this paper, stretch with nearly level surfaces, 

 900 to 940 feet above the sea, along distances of one, two, or three miles. 

 Indeed, by a narrow isthmus of the same plateau deposit joining its two 

 largest areas, it is continuous five miles from south to north. 



Rock Formations beneath the Drift. 

 The Saint Peter sandstone and the overling Trenton limestone form 



* In these studies of lake Hamlin e I have derived much aid from the good topographic maps 

 called the Saint Paul and Minneapolis sheets, with contour lines at vertical intervals of 20 feet, 

 which have been recently issued by the United States Geological Survey. 



