GEOLOGICAL EXI'LOIIATIONS AlfU LITERATURE— 1880. 75 



the Huronian schist is proved conclusively. TIicn- were reg'arded as sed- 

 imentary by the earlier g-eologists, because, as stated by them, they were 

 found to grade insensibly into the "green schists" a.ssociated with them. 

 Wadsworth, however, declares that this is not the case. The massive* beds 

 are distinct from the schists. The contact lietween the two rocks is often 

 sharj), and the one rock does not grade into the other. The large masses 

 of diorite, like that south of Teal Lake, are not interstratified beds, but are 

 true dikes. Thus the origin of these massive beds is set at rest. As to the 

 origin of the green schists so frequently associated with the dikes, nothing 

 is said. It is true that the author found some of the diabase and "diorites" 

 becoming schistose, and others passing into tApical chlorite-schists and 

 hornblende-schists, but the origin of the older schists, tln-ougli whicli all 

 the dike rocks were supposed to cut, has been left unsettled. 



With respect to the origin of the soft hematites, the author is in accord 

 with the majority of those who had studied them. He places them, how- 

 ever, in the same formation with the jasper ores, and not in a different and 

 lower formation, as does Brooks. The soft ores are believed to have l^een 

 formed through the decomj)osition of ferruginous schists by thermal waters. 

 The geology of tlie Salisbm-y mine and its situation seem to the author to 

 lead to this view. The ores are most abundant where the schists, jaspers, 

 etc., are most fractured and shattered, and hence are found in the acute 

 angles between interpenetrating diorite dikes, provided, of course, the 

 "diorite" is younger than the jaspers and ores, as is su])posed to be the 

 case. Near Ishpeming and Negaunee "the dip of the jasper increases as 

 it approaches the 'diorite,' sometimes standing nearly vertical. It was not 

 observed in contact with the 'diorite,' but we feel that the constant uptilting 

 of the jasper and associated schist when near these intrusive rocks is good 

 evidence that the 'diorite' eruption was later than that of the jasper" 

 (pp. 51-52). 



The next problem attacked is the relation of the gi-anite to the Huro- 

 nian schists. If it is intrusive in the schists, it is younger than they and can 

 not be of Laurentian age, as had been thought by earlier writers. The 

 author describes a number of localities where granite veins traverse gneisses 

 and micaceous and green schists, and wdiere, consequently, the granite is 



