598 THE GEOLOGY OF MINNESOTA. 



[Cretaceous beds. 



In section 17, Omro, about twenty miles southwest from the Minnesota river, hornblende 

 schist is exposed in two outcrops. The largest of these lies in the south part of the southeast 

 quarter of this section, covering an area about ten rods long from north to south and six rods 

 wide, and rising ten or twelve feet above the average surface near it. This ledge varies in tex- 

 ture from ordinary hornblende schist to a very compact and hard, black, trap-like rock. It is 

 more hornblendic and more broken by joints than the other outcrop, contains fewer quartzose 

 seams, and for the most part has only thin veins of white quartz, in laminae no thicker than pa- 

 per. The second of these ledges, about a fourth of a mile northwest from the foregoing, extends 

 six rods from northeast to southwest, is from two to four rods wide, and reaches a hight about 

 five feet above the general level. This is much divided by joints and is traversed in many por- 

 tions by thin quartzose seams, which are harder and stand out from a half inch to one inch upon 

 the weathered surface. More rarely this rock encloses here and there veins of white quartz. The 

 dip in both these outcrops is 45 N. W. They are situated in a valley, which is 25 to 40 feet 

 lower than the average hight of the adjoining slightly undulating prairie. It has a width of 

 sixty to eighty rods, and extends from northwest to southeast fully two miles in each direction 

 from these ledges. 



Cretaceous beds. Sandstone, clay, and shale, of Cretaceous age, are 

 believed to underlie the glacial drift throughout the greater part of this 

 district; but their only natural exposures found during this survey are a 

 few low outcrops of sandstone in northwestern Lyon county and north- 

 eastern Lincoln county. Clay and shale, bearing characteristic Cretaceous 

 fossils, have been encountered by wells in Wergeland, Yellow Medicine 

 county, and in Eidsvold and Grandview, Lyon county, townships lying be- 

 tween Canby and Marshall. Though these observations are limited to the 

 central part of this district it seems probable that Cretaceous strata occupy 

 hollows among the Eozoic rocks in Yellow Medicine county, and that far- 

 ther southwestward they attain greater thickness and make the principal 

 mass of the Coteau des Prairies, hidden beneath the thick drift-sheet 

 which everywhere forms the surface of this highland. 



The most eastern outcrop of the Cretaceous sandstone is near the center of section 7, West- 

 erheim, Lyon county, in the west or left bank of the South branch of Yellow Medicine river, 

 about a half mile from its junction with the North branch. A hard, gray, somewhat calcare- 

 ous sandstone is here exposed at several points along a distance of eight or ten rods, rising three 

 to seven feet above this creek. So far as can be seen in these somewhat broken ledges, the lay- 

 ers of this rock appear to be two to three feet or more in thickness and nearly level. In some 

 parts their weathered surface shows concretionary structure, being dotted with roundish masses 

 from an eighth to a quarter of an inch in diameter, which have resisted the disintegrating effects 

 of frost and rains, so that they stand out slightly from the rest of the stone. 



About a mile northwest from this place, numerous blocks of the same sandstone, up to six 

 or eight feet in length, were seen in the channel of the North branch of Yellow Medicine river, 

 in the S. E. \ of section 1, Eidsvold, but no ledge of it in place was observed here. One of these 

 blocks, about five feet long, showing the concretionary character mentioned, contains numerous 

 small flakes and particles of lignite and soft peaty matter. Another has become sculptured by 

 natural agencies, perhaps influenced by some massive concretionary structure, so that in form it 

 resembles the trunk of a tree. Mr. Simon Ilovland, who owns and lives on this quarter-section, 

 believing it to be a fossilized tree, has removed it to a location near his house. The length of 

 this stone is 61 feet, and its diameter at one end is 3J feet and at the other end 2i feet. Its strat- 



