(;e<)L()(;k"al explouatioxs and ijtki;atiirk. 77 



the eiisterii part of the. peninsula, 1ml iiiorc especially because they evidently ()ceii|»y 

 the same geologiea! interval as the typical Canadian seru's, exliiliitiiij; the same noii 

 coufonuity with an uudcrlyinj; j^neissic and granitic system." 



It appears, then, that the only evidence that the Wisconsin geologists Imve that 

 the Laurentiau and lluroniau are what they piir))ort to be is lithologit-al; and tiiciy 

 have advanced no sound argument showing that they Ibrm distiiiel ages in the A/.oic 

 system. The relation of the two supjtosed series is n(.t that which is seen wIkmi tiie 

 Paleozoic comes in contact with the Azoic, or what it would ite natuially were the 

 lluroniau laid down on the preexisting Laurentiau. Tiu; contacts — when these con- 

 tacts have been tigured — appear rather to be those uuide by eruptive rocks witli 

 prior existing ones. The geologists before nu'utioned have assumed, n(»t proved, the 

 sedimentary nietamorphic origin of all the rocks in question, and (ui the correctness 

 of that assumption depends their argument. Tiiey have failed to observe the phe- 

 nomena of the contact when seen beyond tlie mere fact of a diflerent dij) to the? 

 foliation observed. In fact, they have failed to prove any of the jxiints essential to 

 establishing their conclusions. 



Since the questions of tlie uncontornuibility and fault at Penokee <>a]) 

 and of tlie general separa})ility of the Penokee Iron series from the nuire 

 southerly gneisses are fully discussed in subsequent pages of the present 

 volume, it will iu)t Ije needful to consider here at any length the criticisms 

 above quoted. I may merely say in the first i)lace that the PeiMikee fault 

 appears to us entirely demonstrated by the facts presented on the maps and 

 in the text of vol. iii of the Geology of Wisconsin; so that any (juestion 

 as to the existence of this fault becomes a question as to the presentation 

 of facts and not as to the correctness of the conclusions drawn from them. 

 Again, I may say that in case the stratiform arrangement of the gneiss at 

 Penokee gap is a foliation (pressure result) its discordance with the sedi- 

 mentation plane of the overlying slaty series is sufficiently good evidence 

 of an unconformity; and, finally, that the general unconformable jwisition 

 of the Iron series of this region with regard to the more southern rocks 

 seems completely established by the facts presented in the following pages. 



IKVING (K. I).) and Van Hise (C. 11.). On Secondary Enlargements of Mineral 

 Fragments in certain Rocks. Bulletin of the U. S.. Geol. Siu'vey, No. S, ],S84, o« pp. 



Among the special rocks with which the general conclusions of this 

 pamj)hlet with regard to the origin of quartzite are fortified, are from the 

 Penokee region vitreous (piartzite, quartzite-schists, mica-schists, and gray- 



