SURFACE DEPOSITS. 91 



For example, profusely scattered in the drift of all 

 western Iowa we find bonlders of a very hard red qnartzite 

 intermixed with those of granitic origin. Following these 

 northward we are able to trace them step by step until we 

 come upon the original ledges from which they were derived, 

 in the extreme northwestern corner of Iowa and the adjacent 

 parts of Dakota and Minnesota. These ledges belong to the 

 Sioux quartzite formation, described elsewhere in this report, 

 and are the most southerly exposures of that formation yet 

 known. Continuing northward into Minnesota we find these 

 quartzite ledges to disappear, and the quartzite boulders also 

 to disappear from the surface with them, while those of 

 granitic composition remain as plentiful as ever. Going still 

 farther northward into the valley of the Minnesota river we 

 find there extensive ledges of the same kind of granite as 

 that of which the boulders are composed, and no doubt the 

 same ledges from which a part, at least of our Iowa boulders 

 were derived. These granite ledges are found all along the 

 valley of that river from Fort Ridgely to near its source, 

 and similar granite is also known to exist in northern 

 Minnesota, extending as far east as the Mississippi river. 

 Therefore, we are not surprised to know that boulders of this 

 granite are found in the drift of all parts of Iowa. 



But going back to southwestern Minnesota, near where we 

 first found the Sioux quartzite in place, we are able to trace 

 it eastward as far as New Ulm, a town on the Minnesota 

 river, and no farther in that direction. Now no red quartzite 

 boulders are found in the drift of northern Iowa at any point 

 eastward of a line directly south from New Ulm ; but if a line be 

 drawn from that town to Algona, on the East fork of the Des 

 Moines in Iowa, thence down the Des Moines river to the 

 southern boundary of the State, it will describe approxi- 

 mately the eastern limit of their distribution. It thus seems 

 evident that the glacial current which transported these 

 quartzite boulders, at least those along the eastern limit of 

 the region they occupy, was not directly south, but that its 

 general direction was a little east of south until it reached the 



