HISTORICAL REVIEW OF THE GEOLOGY OB" MICHIGAN. 191 



Houghton Kaviue, where the sandstones, generally called Eastern Sand- 

 stones, appear to dip directly and conformably beneath the Copper Bear- 

 ing Series, although I think that in such cases a careful study of suffi- 

 cient exposures will always show sign of faulting and that the contact 

 is really made by an overthrust fault. Finally, there are other places 

 which lend color to the view of Agassiz and rumpelly, where the sand- 

 stone seems to abut against the trap range, as a conglomerate might 

 against the cliff from which it was formed and finally there are num- 

 erous other places where the contact is plainly one of faulting and the 

 beds of the Eastern Sandstones are variously crumpled. Into the de- 

 tails of the long controversv which has been the subject of a special 

 bulletin (No. 23 of the IT. S.' G. S.) I will not go, but will merely state 

 what I consider to be now proved and probable. 



First. There is a large fault and smaller subsidiary faults running 

 along the southeast side of the Keweenawan Range. There is no reason 

 why slipping and disturbance on this plane may not have occurred from 

 time to time down to at least as late as the stresses which produced 

 a small sharp infold of Niagara and Trenton Limestone, in Limestone 

 Mountain not far off. On the other hand it is certain that the disturb- 

 ance there began before the end of the formation of the Eastern Sand- 

 stone which in some cases laps over on the disturbed strata. Not only 

 that, but I consider it quite likely that the disturbance along this line 

 began before the close of the Keweenawan and that the vents from which 

 came some of the Keweenawan Hows may have lain close to this line. 

 It is not without significance in this connection that at Mt. Bohemia 

 we find close to the fault line an old igneous plug which has altered the 

 rocks which it has invaded. 



Another question concerns the origin of the copper. Its association 

 built in alternating layers of calcite and side by side with silver un- 

 alloyed, prove that it was laid down in a wet Avay. The association 

 of copper with similar traps in a great many parts of the world leads 

 one to look to them as in a broad way at least to the source of the 

 copper. The olivine which is so largely decomposed sometimes contains 

 small quantities of copper and nickel, and Pumpelly. without a doubt, 

 ascribed the concentration of the copjjer to downward percolating Avaters 

 which have decomposed the traps and concentrated the copper. In this 

 I am inclined to agree with him, but Smyth looks to deeper seated hot 

 waters for the source of the copper. The copper bearing formation is 

 tilted and fractured but not contorted. The fractures that run across 

 the formation are easy to detect but those which run with the beds are 

 merely slipping of one bed upon another as the leaves of a book Avould 

 slip when bent, or, have the same strike as the beds but a steeper dip. are 

 very hard t<> detect. The progress in mining has, however, shown that 

 they are very wide spread and slickenslides with chloritic Avails are not 

 at all uncommon. I think they guided the copper deposition. There 

 is a theory among practical mining men that the copper occurs under 

 high ground, and if this is true it will favor Pumpelly's theory, for 

 the downward circulation Avould there be most actiA-e. 



The third part of Vol. Ill is devoted to a further study of the sedi- 

 mentaries of the eastern half of the Upper Peninsula by Br. Carl Romin- 

 ger, now a resident of Ann Arbor, who became and remained State 

 Geologist for some tAventy years. He added a good deal to our knowledge 



