PLATE XLV. 



CHISAGO, ISANTI AND ANOKA COUNTIES, 1888. WARREN UPHAM. 



These counties were originally wooded, but with rather scattering and small 

 trees, amongst which oak and poplar were most numerous. Still, there were tracts 

 of gray till and pebbly clay where the forests were larger. Such tracts are in the 

 southeastern and northwestern portions of Chisago county, the northern towns in 

 Isanti and the western in Anoka counties. 



The last act of the glacial epoch in these counties was to spread a vast mantle of 

 gravel and sand, due to the melting of the glacier and the drainage from further north, 

 forming plains similar to the plains mentioned in Washington and Dakota counties. 

 A bayou-like flood of muddy, tumultuous water, partly from the Mississippi valley 

 and partly from the St. Croix, swept over the central part of this district. 



At a somewhat later stage the rivers cut into this gravelly expanse, leaving 

 abrupt margins, and still later were again and again reduced. Thus were formed 

 three or more levels of gravel plains, the uppermost and oldest forming the general 

 upland over most of Anoka county, and the others constituting terraces along the 

 rivers. The uppermost terrace in the St. Croix valley is at about 125 feet above the 

 river, in section 2, Shafer.* 



Earlier than the formation of this sheet of gravel-and-sand, or, to a large extent, 

 cotemporary with it, the ice-lobe, moving from the northwest, was spread over these 

 counties. The result of its action was to lay down a gray till. This till is distinctly 

 morainic, except in its most eastern portions, where it becomes less stony and might' 

 be called pebbly clay. Prior to the spreading of this gray till there had been an 

 interglacial epoch, and the climate had been suited to the growth of forests the 

 remains of which are found in numerous wells in the town of Nessel, north part of 

 Chisago county. Under this interglacial soil, and generally throughout Chisago 

 county under the gray till, is a nearly constant stratum of modified drift derived 

 from the red till, whose manner of origin was probably analogous to that of the gray 

 gravel and sand lying on the gray till, viz.: it was formed by drainage from the ice 

 of an earlier epoch which carried drift from the northeast. This modified red drift 

 is very extensive and spreads through Washington county to St. Paul and into Dakota 

 county. The red till, its source, is equally common, and, as stated in connection 

 with Washington county, constitutes the bulk of the till surface in Washington and 

 Ramsey counties, lying below the modified red drift. 



*The terraces and the general geology of the region of Taylor's Falls have since been the subject of more detailed study 

 by DR. C. P. BEKKET. American Geologist, vol. xx, pp. 346-383; vol. xxi, pp. 139-155, 270-394, 1897, 1898. 



