136 PUBLIC PARKS OF IOWA 



The quartzite, doubtless, underlies both counties, though buried deep 

 by drift and Cretaceous deposits. On Lu Peter's farm near Little Rock, 

 on the eastern boundary of Lyon county, it was encountered beneath 

 the shale and drift at a depth of 360 feet. At Ellsworth, Minn., near the 

 northeast corner of Lyon county, it was found beneath similar material 

 at a depth of 281 feet. Iowa Geological Survey, Annual Report, 1899, 

 pp 98-100 and 105-7. 



THE SIOUX QUARTZITE. 

 By Samuel Walker Beyer, Geologist. 



The Sioux quartzite is a southwestward prolongation of "Minnesota 

 Point." It extends across the northwestern corner of Iowa and under- 

 lies about equal areas in South Dakota and Minnesota. Its extreme 

 eastern limit of outcrop is marked approximately by Redstone, at the 

 junction of the Cottonwood and Minnesota rivers, while its most 

 westerly exposure is near Mitchell on the James river. It has a maxi- 

 mum width of sixty miles extending from Flandreau, its northern limit, 

 to Canton, just within its southern boundary. The formation, although 

 generally concealed by glacial debris and by scattered patches of Cre- 

 taceous, probably extends over an area of more than 6,000 square miles. 



A southwestward extension of the "Coteau des Prairies" traverses the 

 quartzite area at right angles, a short distance east to its middle, form- 

 ing a watershed for the tributaries of the Mississippi and Missouri 

 drainage systems. The crest of the Couteau, at its middle point in the 

 quartzite area, has an elevation of nearly 2,000 feet above sea level. There 

 is a gentle slope westward to the James river, which, in the vicinity 

 of Mitchell, has an altitude of about 1,200 feet. The eastern slope 

 inclines rather more rapidly toward the Minnesota river, where, near 

 the mouth of the Cottonwood, the elevation is considerably less than 

 1,000 feet. The divide which separates the Red river valley from the 

 valley of the Big Sioux lies some distance to the north of the quartzite 

 belt, so that the surface of the formation as a whole pitches southward 

 at a low angle. The Big Sioux river, with its tributaries, drains the 

 major portion of the area covered by the quartzite in Dakota. 



The streams have high gradients, and have deeply incised the region. 

 Rapids and falls are not uncommon. The flood plains are narrow, and 

 in some instances, as along the Split Rock creek at the "palisades" and 

 the Big Sioux at Dell Rapids, there are canyons whose vertical walls 

 range from fifty to seventy feet in height. In both of the above cases, 

 canyon cutting is not confined to the main stream, but is being per- 

 formed by the side branches as well. As an illustration of the sculpturing 

 done by the short lateral branches, may be mentioned a case which oc- 

 curs about one file north of the Palisades. At this point a gulch makes 

 off at right angles from the main stream and extends eastward more than 

 a mile. It is a narrow gorge which, in places, has reached a depth of 

 from seventy-five to nearly 100 feet. This appears the more striking 



