190 



Savage and Ross 1 — Age of Iron Ore. 



A break in sedimentation. 

 Maquoketa shale Feet 



1. Shale, calcareous, hard, in layers 3 to 8 inches 



thick, some of which are strongly laminated.. 8 to 10 



The unconformity between the iron ore and the overlying 

 Silurian limestone is indicated by the uneven plane of contact, 



Fig. 2. 



Fig. 2. View showing the bed of iron ore at Cascade Falls, 5 miles east 

 of DePere. The iron bed. included between the arrows in the picture, rests 

 uncomformably upon the Maquoketa shale, and is separated from the over- 

 lying Mayville (Early Silurian) limestone by a similar unconformity. 



and by the residual character of the upper part of the iron ore 

 which contains a much larger percentage of iron pyrites than 

 the average deposit. The relation of the iron ore to the 

 Maquoketa shale is an unconformable one wherever this con- 

 tact is exposed, the iron ore resting on different levels of the 

 Maquoketa shale. 



