PLATE XLT. 



WRIGHT COUNTY, 1888. WARREN UPHAM. 



Excepting a few doubtful Cretaceous outcrops, Wright county has no exposures 

 of the underlying rocks. Lignite and Cretaceous shale are frequently found in the 

 drift, and in the gravel along the streams, and it is probable that Cretaceous strata 

 exist undisturbed in much of the county. Of the older rocks it is also probable that 

 on the sinking of deep wells the drill would find some of the Upper Cambrian or the 

 red shales of the Keweenawan, such as met with in the deep wells at Minneapolis, 

 and at Glencoe in McLeod county. 



The geological interest of the county, therefore, centers in the drift. It presents 

 no very important features. The county is almost wholly timbered and has a rolling 

 surface, which locally becomes rough, but along the Mississippi and Clearwater 

 valleys are extensive gravel plains and terraces. These terraces are the remnants 

 of a once continuous gravel plain which was formed in the Mississippi valley by the 

 rapid-flowing waters that were discharged from the ice of the glacial epoch, the last 

 sandy and loamy deposits on this plain being formed after the ice was so far with- 

 drawn that gravel could not be transported by the more steady waters. For a long 

 time the Mississippi was swollen by such water and continued to build up these plains. 

 Later, on the shrinkage of the river to its modern dimensions, this gravel plain has 

 been cut into, and in some places largely removed by the river, thus leaving the 

 terraces that accompany it throughout this and other counties. The flat land along 

 the Clearwater river was probably not formed wholly by that stream, but by the 

 Mississippi. Similar flat tracts make inroads on the morainic area, in Silver Lake 

 and in Monticello. Such gravelly plains are found also remote from the river, in 

 other counties, and here, as there, it is probable that the ice of the surrounding 

 upland contributed both the gravel and the water that bore the gravel along, blending 

 with the general flow of the Mississippi only where the waters of the Mississippi 

 extended. In this case there was an extensive bayou, or series of bayous, over which 

 the Mississippi extended in Wright and Stearns counties. 



The Crow river in this county, with its tributaries, is practically destitute of 

 such terraces, having a very sinuous course across the morainic deposits. The north 

 branch of the Crow river, however, within the morainic part of Meeker county, is 

 accompanied by an extensive gravel plain at Litchfield. Such catch-basins, filled 

 with water, would prevent the formation of gravel plains along the lower reaches 

 of the valley. 



There are two till sheets involved in the drift of the county. The lower one is 

 red, or reddish, and the upper one is gray or bluish gray, but they grade into each 



