236 F. W. SARDESOX THE REDSTONE QITARTZITE 



the Big Cottonwood formation passes the river at that place in a general 

 easterly direction from New Ulm. By reason of dip, the Cretaceous 

 would lie below the river. 



North of the Big Cottonwood the glacial drift is sufficiently intact to 

 leave the question of former and present relation of the Cretaceous rocks 

 greatly obscured. But, in the valley of the Minnesota river, the drift 

 appears to extend down in place of the Cretaceous, from north of New 

 Ulm, 10 miles to a place (some 6 miles north from the Big Cottonwood 

 valley) where fresh granitic rock rises 25 feet above the river. Evidently 

 l)oth the Cretaceous rocks and the Archean granites have been greatly 

 eroded there in post-Cretaceous, pre-Glacial time, and apparently a drift- 

 filled valley crosses the course of the Minnesota river. At Sleepy Eye, 

 which is north of the Big Cottonwood river, the granitic rock is said to be 

 found in a well at a depth of about 200 feet — that is, at 800 feet above 

 tide — no Cretaceous intervening between it and the drift. Absence of 

 rotted granitic rock argues post-Cretaceous erosion. 



Glacial Drift and Eiver Deposits : Quaternary 

 character of the drift 



The drift in the region about Bedstone is mostly of boulder clay or 

 till, although modified drift — gravel and sand — regularl}^ accompanies 

 the till. ■ All the older rock formations of the region were doubtless once 

 covered by glacial drift, as they are yet, excepting in the river valleys. 



The surface of the drift outside of the river valleys is marked by irreg- 

 ular hills and closed basins, such as are characteristic of the glacial drift 

 of the Wisconsin stage, but these irregularities occur with such monotony 

 as to give the country the aspect of a nearly level land, sloping gently 

 toward the Minnesota river. Two or 3 miles from the river the average 

 altitude of the land surface is at or above 1,000 feet above tide, while 

 along the border of the Minnesota valley few points only reach to 1,000 

 feet. One such point within the city limits of New Ulm is 1,015 feet. 



The drift averages about 200 feet thick, but is far from uniform, be- 

 cause of the surface irregularities and the unevenness of the rock base 

 upon which it rests. Bedstone hill has the highest known rock subjacent 

 to the drift. There the Courtland quartzite formation has been covered 

 about 50 feet by till. The Big Cottonwood formation was covered from 

 100 to 150 feet deep. Northwest of New Ulm the drift appears to extend 

 to or below the river level, or 200 feet deep. The Big Cottonwood river 

 cuts through the drift into the Cretaceous rocks for at least 7 miles 

 above its mouth and probably all the way from Springfield, the till and 

 associated gravel beds being 100 to 150 feet thick, as seen in the bluffs. 



