Junction of Primordia I Sandstones and Huronian Schists. 139 



ON A HAND SPECIMEN, SHOWING THE EXACT 

 JUNCTION OF THE PEIMORDIAL SANDSTONES, 

 AND HUHONIAN SCHISTS. 



BY ROLAND IRVING, A. M., E. M., 

 Professor of Geology ia the University of Wisconsin. 



On Black River, in Jackson county, this state, in the vicin- 

 ity ot the town of Black River Falls, the Primordial sand- 

 stones are found overlying Huronian and Laurentian rocks. 

 About a mile or two above the town the banks of the river 

 are formed of abruptly rising and as abruptly sinking mounds 

 of tilled Huronian schists, — chloritic, talcose, talco siliceous, 

 siliceous and ferruginous. Between these mounds, the de- 

 pressions are filled with the light colored quartzose Primordial 

 sandstones of the region, and these often form the bank of the 

 stream. So close is the association of these formations, that in 

 following the bank of the stream, one is constantly stepping 

 from the Primordial sandstones, on to the Huronian schists, 

 and then as abruptly back again. In many cases the sand- 

 stones form the upper part of a high bank, whilst below, im- 

 mediately at the water's edge the schists are visible. In these 

 cases the exact junction of the sandstone and schists is nearly 

 always concealed by debris, soil and undergrowth. In one 

 place, however, Mr. T. B. Bowman, assistant on the geological 

 survey, found a long exposure showing the exact line of junc- 

 tion, the horizontal sandstones above, and the ferruginous 

 schists below. From this place he obtained specimens, of 

 which I exhibit one. It will be noticed that even the hand 

 specimen shows the horizontal position of the sandstones and 

 the inclined position of the schist, or "iron ore" the lamina- 

 tion being marked. (See sketch.) 



