538 GEOLOGY OF CENTRAL WISCONSIN. 



about Devil's Lake, the high level sandstones, with bowlder-conglom- 

 erate beds, are again found, with a total thickness exposed of over 300 

 feet, the base being nearly on a level with the lowest of the limestones 

 at the locality just described. In one place, a short distance north- 

 east of Devil's Lake, large loose masses of this sandstone occur at an 

 altitude between 100 and 150 feet above the last named limestone, 

 carrying fossils, among which are Dicellocephalus Minnesotensis and 

 others supposed to indicate the upper layers of the Potsdam series. 



For these anomalous occurrences, which will be more fully under- 

 stood from a study of the sections of Plates XIX and XX, and Figs. 

 48 and 49 of this volume, and of the detailed descriptions in the fol- 

 lowing pages, it is not easy to find a satisfactory explanation. It ap- 

 pears altogether inadmissible to attribute the great elevation of the 

 high-level sandstone to a sudden affection of the nearly horizontal 

 strata by a violent northern rise as they near the quartzite ranges. 

 This supposition is forbidden by the utter lack of any indication 01 

 such a rise in the large exposures that occur; by the normal success- 

 ion of beds that holds true in all the region east, west and north of 

 the quartzite ranges; and by the great amount of rise that would be 

 necessary. In "Westfield it would have to be 300 to 400 feet to the 

 mile. Moreover, within the space enclosed by the quartzite ranges, 

 as described, occur the Lower Magnesian, Madison and Mendota, in 

 their normal succession, and with their normal lower level, whilst in 

 one case the limestone and perfectly horizontal high-level sandstone 

 are so near by that no amount of dip could possibly account for the 

 occurrence. It may be regarded as beyond question that entirely 

 non- calcareous sandstone w r ith bowlder-conglomerate and Potsdam 

 fossils does, not only apparently, but actually, occupy the whole space 

 between the horizon of the base of the Mendota, and that of the sum- 

 mit of the Lower Magnesian. 



It might be supposed that the wear of the quartzite ranges contin- 

 ued to produce sandstone and conglomerate beds during the growth 

 of the limestone in the deeper water near by, but the suddenness of 

 the transitions, the occurrence of Potsdam fossils in the sandstone, 

 and the existence of the limestone layers close to and within the 

 quartzite ranges, appear great difficulties in the way of such an ex- 

 planation. That the high-level sandstones represent really an older 

 series, upon whose eroded upper surface rest the calcareous sandstone 

 of the Potsdam, the Mendota, the Madison, and the Lower Magnesian, 

 as indicated in the ideal sketch of Fig. 34, appears a more satisfactory 

 explanation, but one which meets a considerable difficulty in the oc- 

 currence of upper Potsdam fossils in the high-level beds, and one 



