26 THE I'ENOKEE IRON-BEARlN(J SERIES. 



It is supposed by geologists tliat slate rocks were oiigiiially lU'iJOsited from 

 water, and that the layers were at tirst nearly horizontal. Whatever may have been 

 the origin and original position of this slate, the same must be assigned to the iron 

 ore, the same eauses continuing to operate throughout the whole i)eriod of the forma- 

 tion of the slates and the iron. 



These strata have all been tilted or lifted up from the horizontal to neaily a 

 vertical position, without otherwise materially modifying their structure and composi- 

 tion. That iiart of the slaty deposit which rests upon, and was therefore of later 

 formation than the iron, has been subjected to still other iutiaeuces (i)robably heat 

 and pressure), which have transformed the fissile slate into a very hard subcrystal- 

 line rock. 



The geological relations of this prolonged ore bed are quite the same as thf>se of 

 the nonmagnetic ores near Marquette. We have the same granitic rocks at the 

 north, the same quartz rocks at the south, and the same slate in which the ore is 

 found. Hence we nmst assign to each a similarity of origin, and whatever theory 

 may be adopted for one must bo equally true of the other. (Pj). 26-29.) 



The following' quotation is of interest as showing that Dr. Lapham 

 was the first to notice indications of the occurrence at Penokee gap of the 

 fault whose existence was subsequentl)" demonstrated and details worked 

 out by the Wisconsin Survey.^ 



The range here appears to have made a sudden offset northward in ]iassing the 

 river, and the strata are more or less disturbed, the dip and direction not being so 

 uniform and regular as at most of the other localities examined. 



Dr. Lapham held, with regard to the \alue of the strongly magnetitic 

 rocks of the Penokee range, the usual unfortunately favorable opinion which 

 later experience has not justified. 



It will be seen that we have already discovered good ore in such quantities as 

 to be practically inexhaustible, situated at points accessible to water |)ower and 

 having Itold fronts, rendering it comparatively easy to be quarried. For many years 

 to come only the richest and most accessible ores can be brought into use, rejecting — 

 at least for the present — all such as have too large a proportion of silica, and such as 

 are not in a condition to be easily and cheaply removed from the natural bed. 

 Tiiough it is clearly shown that the ore is coextensive with the range, yet it must not 

 be supposed that it constitutes a continuous workable mine throughout this whole 

 distance of 20 miles. It is only at the i)oints indicated where the ore is easily worked 

 and where water power is at hand that very great immediate value can be put upon 



' Geology of Wiscousiu, vol. 3, pp. 150-152, and Atlas, Plate xxni. 



