330 



GEOLOGY OF EASTERN WISCONSIN. 



rest of the deposit. It is dark purple in color, raucli harder and more 

 compact than the oolitic ore, and is not lenticular, though sometimes 

 incorporating a few concretions. It gives a bright scarlet streak and 

 powder, has an irregular or conchoidal fracture, and much higher 

 specific gravity than the main mass. It contains, as noted by Br. 

 Percival, scales of specular ore. 



At the mines, the bedded ore varies from 15 to 25| feet in thick- 

 ness. To this, at the Mayville Ore Bed, there is added a considerable 

 depth of drift ore increasing the thickness to 40 feet or more. 



Fig. 41. 



Pbofilb Section at the Matvillb Oee Bed. 

 a. Cmciunati Shale. J. Budded Ore. t. Drift Ore. (i. NiagaraLimestone, Capping Ore. /. Mixed 



Drift. 



The accompanying section (fig. 41) shows very inadequately the ar- 

 rangement of the undisturbed and drift ores, and of the ocherous 

 drift, gravel, bowlders, and disturbed and undistui-bed limestone, as 

 seen at the time of my visits. It was taken just when, the drift, in 

 the progress of mining, was giving place to undisturbed limestone, a 

 point most favorable for study. It will be noted that the various 

 bands of drift material extend from the left (north) obliquely upwards 

 to the right, and that at the left, the upper dark layer of ore is sWept 

 away, and at the right, it is broken up in a peculiar way very imper- 

 fectly illustrated in the figure. 



The force that produced the disturbance and intrusion of the ore 

 into the common drift seems to have come from the west of north, 

 and to have been massive in character. It is but another characteris- 

 tic instance of glacial action. 



What may have been the original extent of the ore deposit to the 

 westward cannot now be ascertained. That portion has been swept 

 away by the denuding agencies which formed the valley lying in that 

 direction. To the southward and south-westward, the same agencies 

 have limited our knowledge. To the eascward, the deposit thins out. 

 To the northeastward, there rises a high ridge, underlaid by a consid- 

 erable depth of limestone, which has thus far limited explorations in 

 that direction, since the immense quantities of ore already developed 

 leave no necessity for further exploration at present by the company 



