C. R. Stauffer — The Minnesota Devonian. 397 



ments are all found in southern Minnesota and may indi- 

 cate a somewhat greater extent of the present Devonian- 

 covered area rather than the existence of other Devonian 

 areas. Over the great ridge area of the buried Minnesota 

 mountains the Devonian fragments in the drift are some- 

 what smaller and usually less abundant. Hence it seems 

 probable that these scattered limestone bowlders and 

 loose Devonian fossils have been brought down by the 

 Pleistocene glaciers from the great outcrops of Devonian 

 in the vicinity of Lake Winnipegosis and Lake Manitoba, 

 and that the Minnesota Devonian deposits are confined to 

 the southern part of the state. 



The Devonian, as outcropping in the southern part of 

 the state of Minnesota, consists chiefly of limestones of 

 varying purity. Probably the great body of it runs as 

 high as 17% to 18% Mg00 3 but occasionallv layers are 

 found with 97% to 98% CaC0 3 and only a fraction of a 

 per cent of MgC0 3 . The "best outcrops are to be found 

 in the central and southern parts of Fillmore county 

 where the Devonian is usually exposed in every highway 

 cut. Where both the top and the bottom show, the 

 Devonian apparently rests disconformably on fossili- 

 ferous Maquoketa shale (Ordovician) and usually has no 

 covering other than the drift. In the vicinity of Austin, 

 however, the uneven upper surface of the Devonian lime- 

 stone is covered by eight to ten feet or more of rather 

 soft gray to red clay which has usually been classified as 

 a Cretaceous (3) deposit, and which it probably is as clays 

 and lignitic beds of that age have been reported in the 

 deeper wells of Freeborn county to the west. However, 

 some of the similar clays of central and southern Min- 

 nesota contain glacial pebbles and are undoubtedly of 

 glacial origin. It has been suggested .that a remnant of 

 the higher Devonian shales may occur in western Mower 

 county and perhaps in certain parts of Freeborn county, 

 but up to the present this has not been certainly deter- 

 mined. The Western margin of the Devonian is lost 

 under a covering of drift which in Freeborn county has 

 been estimated to have a thickness of one hundred feet, (4) 

 with perhaps even greater thicknesses in the adjacent 

 county (5) to the west. There is thus little hope of contin- 

 uing the Minnesota Devonian section, except by the drill, 



