126 Wisconsi7i Academy of Sciences, Arts, and Letters. 



ing quartzlte show most unmistakably the effects of shore 

 action. The quartzite is generally in place, but the large 

 blocks, formed by the crossing of the planes of bedding and 

 the joints, are somewhat isolated, as if they had formed crags 

 on an old coast, where the wearing of the waves had enlarged 

 the cracks. Into these fissures and crevices the sand is forced. 

 There are also blocks of quartzite, that have been displaced 

 somewhat, which are enveloped in sandstone. In the sand- 

 stone itself is an occasional rounded pebble of quartzite. The 

 sandstone which rests upon the northern flank is irregularly 

 bedded, having the ebb and flow structure. Further north 

 are these isolated hills of sandstone. 



Eesting on the sandstone at the south, and stretching also 

 over the quartzite, is a conglomerate made up of a friable 

 sandstone, like that below, containing numerous rounded peb- 

 bles of the quartzite of obvious sizes. The cement makes up 

 a considerable part of the rock. This coglomerate, as I have 

 assured myself by careful examination, is exactly like that 

 mentioned by Mr. Irving, as occurring on the quartzite just 

 northeast of Devil's Lake, and containing Potsdam fossils. 

 The finding of this conglomerate, therefore, in its true rela- 

 tion, verifies Mr. Irving's supposition in opposition to Mr. 

 Winchell, that neither the conglomerate nor the quartzite is 

 the base of the Potsdam system, for here the true base comes 

 in between, as sandstone. 



In the same manner there is a conglomerate at the north, 

 resting conformably on the sandstone and unconformably on 

 the quartzite. One of the isolated hills of sandstone is also 

 capped by the same. Though on the same level as the con- 

 glomerate at the south, its character is different. It is made 

 up almost entirely of small rounded pebbles of quartzite of a 

 pretty uniform size. The cement is quite hard, but true sand- 

 stone. 



This section, then, represents an old Azoic reef of tilted 

 rock, running east and west, washed upon either side by the 



