PLATES (PAGES) XIX AND XX. 



COTTONWOOD AND JACKSON COUNTIES, 1884. WARREN UPHAM. 



Extending from Watonwan county westwardly into Cottonwood county is a 

 prominent plateau caused by the Potsdam quartzyte. It runs to the western part 

 of Storden a distance of about twenty-two miles in this county, where it disappears 

 gradually by flattening out and running below the drift. The width of this ridge, 

 as a known quartzyte range, varies from two to seven miles. Structurally it is a 

 monocline, with a dip toward the south, becoming nearly horizontal toward the 

 west. The rock is hard and very refractory, but, judging from the use that is made 

 of the same rock at Sioux Falls, it could be put to extensive use in construction if it 

 were treated systematically and thoroughly. At the exposed surfaces it is much 

 broken by jointage, and it also carries small beds of catlinyte, like that at Pipestone. 

 Some of the sedimentary layers are massive, reaching two feet in thickness. As a 

 whole this rock might be considered the southerly arm of the anticline which shows 

 its northern arm at Redstone, near New Ulm. This formation probably extends 

 much further south, under the drift. The ridge rises on the north side rather 

 abruptly, about 100 feet at the east end and 300 feet at the west, the full hight reach- 

 ing 1,500 feet above the sea. 



Toward the south and southwest this elevation is for the most part maintained, 

 and even increased, so that the Little Cottonwood river and a fork of the Watonwan 

 river now northerly across the quartzyte plateau, rising on the drift surfaces further 

 south. It may be presumed that this plateau of quartzyte extends southwestwardly, 

 though covered by drift and by Cretaceous strata, then westwardly and northwest- 

 wardly giving the primary basis for the Coteau des Prairies. On this plateau the ice 

 piled its marginal and medial moraines, but in its southern swing passed over it, 

 leaving only a rather uniform layer of till. Quartzyte was struck in the deep well 

 at Heron Lake at 186 feet. 



The most of the rest of Cotton wood and Jackson counties consist of smooth or 

 undulating till, though considerably diversified by streams and lakes, which always 

 introduce bluffy shores and more or less timber. 



There is, besides, a prominent belt, of roughly morainic contour, which crosses 

 the central part of Jackson county north and south, from three to six miles in width, 

 the most conspicuous portion of this range being the Blue mounds, northwest of 

 Windom, from which the belt runs northwestwardly into Murray county. A spur 

 from this belt extends, probably as a medial moraine, from Windom northwardly 

 about twelve miles. The western portion of these counties rises to over 1,500 feet, 

 the eastern from 1,100 to 1,400 feet. 



