344 T HE GEOLOGY OF MINNESOTA. 



name indicates, has been worked over by water since its deposition in the 

 drift. It occupies low pond-like spots, or abuts on thej)luffs. It is usually 

 of a uniform reddish-yellow color and quite arenaceous. Sometimes it is 

 in colored layers of red, yellow and green. In this case its derivation is 

 probably from the green shale of the Trenton as well as from the drift. 

 The washed clay is used for brick. 



The exposures of sand and gravel are not extensive in the parts of 

 the county examined by me. Where seen they exhibit the usual char- 

 acters. The boulders are entirely absent in most parts of the county. In 

 many scattered localities, again, they are abundant; and in the southwest 

 corner of the county they are often found of great size. 



About a mile and a half northeast from Marion are scattered boulders 

 of siliceous iron ore, having the characters of the iron ores seen in the 

 Mesabi iron range, and similar to some siliceous iron seen in the Black hills.* 

 These pieces are not frequent. They lie on the brows of the Trenton ter- 

 race, and are associated with other drift boulders. Some of them show 

 really very little iron, but partake more of the nature of the non-ferrugi- 

 nous quartzyte of the Potsdam, though still of a reddish color. There is 

 not that topographic surface here that indicates the immediate presence 

 of the formation in outcrop, but these pieces are on the Trenton and 

 among the drift, which rather shows that they have come with other 

 drift from some point farther north. 



In the museum of the University is a magnetic boulder of siliceous 

 iron ore, known as lodestone, presented in 1875 by James Hinton, said to 

 have been found in the neighborhood of Quincy, Olmsted county. Be- 

 tween St. Charles and Quincy are many evidences of northern drift in the 

 form of hornblendic and granitic boulders. They are often met in wells 

 and cellars, though the country here is covered with a loam-soil of a black 

 color. 



The following table of wells will be useful for an analysis of the drift. 

 The facts were furnished by 0. Sprague, practical well-digger: 



Hepoi t of it i cconnoissmiue of the Black hills, Ludlow, 1874, pp. to, it. 



