SOUTHWESTERN MIXXESOTA. • 89 



white kaolin, clouded with blue clay, aud containing some grit, 25 feet; 

 and white quartzitic sandstone, 28 feet, containing kaolinic material in its 

 lower part, "apparently resulting from the decay of grains of feldspar 

 after deposition in the sandstone."^ 



The thickness of 446 feet of principally dark beds, lying between 

 1,238 and 792 feet above the sea, probably corresponds to the Fort Benton 

 shales and Dakota sandstone, containing lignite and impressions of leaves, 

 on the Cottonwood and Minnesota rivers, where their elevation is approxi- 

 mately 800 to 1,000 feet above the sea. Under these the thickness of 79 

 feet of mostly white kaolinic clay or shale and sandstone, constituting the 

 base of the Dakota formation here, appears to be the same with the deposits 

 of white and greenish clay, often sandy and gritty, which lie in water- 

 worn hollows of the Cambrian strata along the lower part of the Minnesota 

 River. These earliest Cretaceous sediments were evidently derived from 

 erosion of decomposed surfaces of the adjoining Archean gneiss and granite. 

 Not all of this decayed and kaolinized rock was worn away then nor by 

 the later erosion of the Glacial period; for at many places in the Minnesota 

 Valley, along the distance of nearly 50 miles between Granite Falls and 

 Fort Ridgely, it forms the upper 10 to 20 or 30 feet of the Archean 

 outcrops. At 713 feet above the sea-level the Cretaceous deposits of Tracy 

 rest on reddish granite of Archean ag-e, into which this well was drilled 34 

 feet, to a total depth of 724 feet. 



In the village of Browns Valley, situated between Lakes Travei-se and 

 Big Stone, in the channel of which Lake Agassiz outflowed southward, a 

 well has been sunk to the depth of 465 feet, extending from 975 to 510 

 feet, approximately, above the sea-level. The general surface on each 

 side of this valley or channel is about 1,100 feet above the sea, 125 feet of 

 glacial drift having been eroded above the site of the well. After passing 

 through an undetermined thickness of alluvial and drift deposits, this well 

 penetrates dark-bluish, hard clay or shale to the dej^th of 360 feet; a black 

 layer of lignitic shale, 2 feet; gravel and sand, alternating with layers of 

 blue clay, 58 feet; quartzitic sandstone, 5 feet, from above and beneath 

 which artesian flows of water are obtained; greenish, micaceous, and kaolinic 



' Geol. and Nat. Hist. Survey of Minuesota. Fourteenth Annual Report, for 1885, pp. 351-353. 



