PLATE LVIT. 



AITKIN COUNTY, 1899. WARREN UPHAM. 



There are but three outcrops of the bedrock in Aitkin county. There is a 

 quartzyte at the west side of Dam lake, in Kimberly, and a "diabase" about three 

 miles toward the southwest, at one-fourth mile west from the south end of Long lake. 

 There is granite in full force on the Snake river near the south line of this county, 

 but in Kanabec, and at points between Snake river and Cowan's brook in Aitkin 

 county, it is near the surface, as indicated by numerous blocks of a fine-grained, gray 

 granite, seen in the glacial drift. The quartzyte has a length of outcrop of about 

 250 feet along the shore, and varies in width from fifteen to fifty or sixty feet, rising 

 to a hight of four or five feet above the lake. It is so broken into blocks that no 

 compact ledge is seen. The rock is a coarse quartz sandrock, or quartzyte, some of 

 the grains having a lavender color, and there is but little doubt that it belongs to 

 the same formation as the quartzyte at Pokegama falls, which is associated with the 

 hematite ore of the Mesabi range. (See, however, the Pokegama Lake plate. ) 



The "diabase" is three miles southwest from the quartzyte and occurs on both 

 sides of Long lake. It is really a very dark-colored, hornblendic gneiss, with biotite 

 and a white and rarely pinkish feldspar resembling orthoclase. This rock presents 

 the aspect of much of recrystallized Keewatin (or Coutchiching), and is quite certainly 

 a part of the Archean and underlies the above quartzyte nonconformably. 



The drift of Aitkin county would average probably between 100 and 150 feet in 

 thickness. It is evidently from the north and northeast, but there is reason to believe 

 that a considerable Cretaceous element, sometimes in the form of lignite, was also 

 mingled with the drift. The till is prevailingly dark and somewhat bluish gray, 

 except in the southeastern part of the county, where it has a reddish tint. 



Morainie tracts are found in the northern part of the county and also in the 

 southwestern, representing the Fergus Falls and the Leaf Hills moraines, as inter- 

 preted by Mr. Upham, but a larger part of the county is covered with a smoothly undu- 

 lating or flat till sheet. Through the central portion, however, is a belt of sand and 

 gravel, extending north and south, and along the Mississippi, the Willow and other 

 valleys is a thick deposit of fertile post-glacial alluvium. 



A small glacial lake, named lake Aitkin by Mr. Upham, covered much of the 

 township of Aitkin. It probably extended also across the Mississippi northwest- 

 wardly, including much of the valley of Willow river. It was probably due to the 

 long-continued existence of a glacial lobe in the basin of lake Superior, which was 



