190 SEVENTH REPORT. 



transit line was nsed also as a bench-mark and is 685 ft. above the lake. 

 Another point about two and a half miles from the lake is GOO ft. above 

 it, so that there is a decline of only 85 ft. in the first 11 miles. In the 

 remaining distance there is a fall of GOO ft. the last 100 being the height 

 of the lake hill. On the whole, the road has not many hills, and no very 

 bad ones, save that just spoken of, which is steep. The next largest is 

 just south of the D. S. S. & A. K.. Ry., and is one which Bessemer people 

 have to go over in going to and from North Bessemer which is their 

 passenger station for the D. S. S. & A. R. Ry. Tiiis hill is also just 100 

 ft. high but is not so steep as the lake hill. 



Bessemer is on the Gogebic iron range, and is underlain by rocks of 

 that series, but the ridge just to its north exposes Keweenawan rocks. 

 The nearest Penokee exposures to the Keweenawan rocks are gray- 

 wackes, which strike nearly east and west and have a dip of 55° to G0° N. 



The first exposures above the grayAvacks are of red sandstone, whose 

 vitreous appearance makes it somewhat resemble a quartzite. This sand- 

 stone is the basal member of the Keweenawan series. 



The work of geologists, such as Van Hise in his Penokee-Gogebic 

 monograph puts an unconformity between the iron-bearing and the cop- 

 per-bearing rocks above them. The exposures near Bessemer do not war- 

 rant the saving that there is an unconformity, nor do they warrant the 

 saying that there is not. The rocks are not exposed along the contact, 

 there being a width of at least one-half mile unexposed. Concerning 

 conformity, or unconformity, one can say nothing from the area worked 

 bj' us. 



The basal sandstone of the Keweenawan dips 70° to 73° N. There is a 

 surface exposure of 200 ft. How much of the drift covered area is under- 

 lain by sandstone, and how much by graywacke cannot be said. 



Above this sandstone is a thick series of eruptives. The sedimentaries 

 of the Penokee and the basal sandstone of the Keweenawan represents 

 a period of quiet, but the great thickness of eruptives in the base of 

 the Keweenawan marks a change. There is exposed almost continuously 

 a surface width of 8600 ft., which with a dip of 70° means a thickness 

 of 8000 ft. of eruptives. Following is a surface width of 13000 ft. with- 

 out exposure. Since the dip gradually decreases as we go north it is 

 not at all probable that this area is underlain by rocks that have an 

 average dip greater than 65°, which would give a thickness of 11800 

 of rock. This area is probably underlain by eruptives, since such rocks 

 are exposed on either side, yet it is not at all certain that there are not 

 some sedimentaries. Beyond the unexposed area are eruptives with a 

 surfaced width of 19000 ft., which if we allow to di]) of 56° N., gives 

 us a thickness of 15600 ft. Here then is a total thickness of 35400 ft. 

 in which the rocks are practically Avholly basic eruptives. 



Above these basic eruptives is a felsite whose exposed width is 660 ft., 

 and it cannot exceed 2000 ft. The known thickness is 460 ft., since its 

 dip is 45°, and it cannot exceed 1400 ft. The resisting power of this 

 felsite has enabled Chippewa Bluff to stand against the degrading 

 agencies of nature. 



Above the felsite there is a series of interbedded sedimentaries and 

 eruptives. These have a surface exposure of about 9000 ft. With an 

 average dip of 37° there is a thickness of 5400' ft. The top of these 

 interbedded eruptives and sedimentaries takes in the last eruptives 



