PLATE XLIV. 



WASHINGTON COUNTY, 1888. N. H. WINCHELL. 



On the eastern and southern boundary this county is surrounded by deeply 

 excavated gorges, occupied by the St. Croix and the Mississippi rivers. The water 

 surface in these gorges is from 250 to 300 feet below the adjoining uplands. The 

 rocks cut by these excavations are, near the brink, limestones and sandstones of the 

 Upper Cambrian, but at a mile or two back from the brink the St. Peter sandstone 

 and the Trenton limestone give a further elevation, which, at Lakeland, carries the 

 surface to 383 feet above the St. Croix. 



The immediate bluffs of these valleys are frequently composed of gravel and 

 sand, which forms terraces bordering both valleys, rising, at Lakeland, to the maxi- 

 mum hight of 233 feet above low- water level of the St. Croix. The gravel strewn at 

 this altitude is comparable with the gravel forming elevated plains in Dakota county, 

 such as those of Rosemount, Nininger and Marshan. Extensive elevated gravel 

 plains of this kind characterize the southeastern part of Washington county. They 

 were formed probably when the ice of the last glacial epoch was still present in the 

 morainic tract further north and west, and supplied the till from which the rapid 

 drainage washed out the gravel, carrying the clayey ingredient to more southern 

 latitude. These higher plains can hardly be attributed to the action of the river 

 proper, but to that earlier stage of glacier drainage when the rivers had not yet 

 taken form, but when the waters spread widely everywhere at all levels, springing 

 directly from the dissolving glacier. At lower levels are more constant and distinctly 

 fluviatile terraces. One is about 130 to 150 feet above lake St. Croix and another 

 about seventy-five feet above the same-. 



These plains are separated from the northwestern part of the county by a rolling 

 belt of moraine of red till which is the northern extension of that of Dakota county. 

 It runs to the vicinity of Taylor's Falls, in Chisago county, and leaves the state. 

 This rolling belt of red till drained southwardly in the southern part of Ramsey 

 county, but on the north side of the Ramsey county divide, owing to the natural 

 slope being northward, and the damming up of the northward outlet by the contin- 

 uance of the glacier further north, a small glacial lake was formed over the region 

 north and northwest from White Bear lake, extending to Centerville and probably 

 further, and covering Forest Lake and Oneka in Washington county. This was 

 probably a fluctuating lake, thus forming no distinct beaches, yet its outlet a portion 

 of the time of its existence was probably through Big Marine lake toward the south 



