542 THE MAEQUETTE IROX-BEAEING DISTEIGT. 



mine. Hence, on Brooks's assumptions, there is displacement on both sides 

 of the trough at the line of the river, and a fault is clearly indicated. 



It is susceptible of demonstration, however, that no fault exists involv- 

 ing the Groodrich quartzite. On the northeast side of the fold the contact 

 of the upper quartzite on the lower series, which is a surface of economic 

 interest, has, since the time of Brooks's studies, been definitely fixed at 

 numerous points on both sides of the river where it is not naturally exposed 

 by diamond-drill borings. These points, when accurately platted, fall on a 

 line which shows no displacement at the liver. 



At the southwest side of the fold the upper quartzite is abundantly 

 exposed on both sides of the river, and its base has been located at inany 

 points in the West Republic mine, under the river, and in several test pits 

 and di-ill holes on the western side. The platting of these data shows 

 conclusively that no displacement can exist which has heaved the upper 

 quartzite to the extent of 100 feet. 



The disappearance of the lower series onrthe west side of the river, on 

 the southwestern side of the fold, presents, however, a real difficulty. That 

 its absence is due to a sudden bending of the strike toward the northeast is 

 very improbable, because in the few outcrops of the iron-bearing member 

 nearest the river there is almost perfect conformity in strike with the upper 

 quartzite. Also, underground in the West Republic mine, the jasper was 

 followed nearly to the west bank of the river. It seems necessary to believe, 

 therefore, that the formations of the lower series continue without sensible 

 change in sti-ike as far as the river, and there terminate squarel}' against 

 the granite. Such relations can be best explained by supposing that the 

 granite on the west bank either had intruded the lower series or had been 

 brought to the level of the old surface by a fault before Upper Marquette 

 time. Between these two explanations there is no present means of 

 choosing. 



On Brooks's map, ali-eady referred to, a tongue of the upper quartzite 

 is represented as forking from the main mass of the same rock and running 

 northwest along the top of the Republic bluff, a thin wedge of the under- 

 lying specular jasper being interposed between them. No explanation of 



