SANDSTONES CHARACTER AND DISTRIBUTION 



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purity. At most typical localities the composition is about 99 per cent 

 SiO,. In color there is considerable variation, locally, chiefly due to 

 iron stains, but at the typical exposures it is white or yellowish, often 

 only faintly streaked with color. 



Usually the rock is massive, with only occasional bedding planes or 

 color zones or other structural features. 



This formation, considering its exceptional character, lias very wide 

 distribution. Its outcrops occur along a zone including southeastern 



Figure 1. — Areal Distribution of the Saint Peter Sandstone Formation 



Minnesota to the vicinity of Minneapolis and Saint -Paul, southwestern 

 and southern Wisconsin and a narrow fringe along the eastern margin of 

 that state; a like strip across the northern peninsula of Michigan, passing 

 into southern Canada in the vicinity of Saint Joseph island, continuing 

 in an easterly course. It has a most tyjDical development in northern 

 Illinois and portions of eastern Iowa. There are also outcrops of the 

 same formation in Missouri. 



