GEOLOGICAL EXPLORATIONS AXI) LITERATUEE— 1803. 139 



The Repul)lic formation as a whole is separated from tlic Cascade 

 formation below and from the Holyoke formation al)ove l)y (•()n<ilomcrates 

 and unconformities. The conjrlomerates are well known at a nundier 

 of places. Objections are raised to the acceptance of Irvinii's tiieorv of 

 the origin ot the ores from an oriii'lnal ferrniiinous carbonate, since it is 

 believed that the carbonate is itself secondary and that the phenomena of 

 alteration reported are "due to surface action on the iron-bearin<i- sc-liists." 



More detailed accounts of tlu? eruptive rocks cutting;- tlie h'epublic 

 formation are given in this report than in the abstracts alread}- r(4erre(l to. 

 Granites, felsites, diabases, diorites, and porphyrites are all reco<i-nized 

 as intrusive in the Repuljlic i-ocks. Many of the green schists of the 

 formation are thought to be eruptive, though it appears tliat some ol' them 

 are still i-egarded as sedimentary-. 



The porodites, or volcanic asluis, are common in botli the Repul)lic and 

 the Holyoke formations, though "more apt to be seen in tlie former." 



In treating of the Holyoke formation Wadswoith refers to his former 

 belief that Brooks's (piartzit(^ tongue in the iron formation at lve})ul)lic Is 

 an eruptive greisen. He now corrects this earlier statement and acknowl- 

 edges the rock to be quartzite, but supposes the iron-schists below and above 

 this tongue to be of different ages. The former he regards as He})ublic and 

 the latter as Holyoke. At this place and at several other localities there 

 were observed in the Republic rocks fissures filled with Holyoke sediments. 

 These the autlior proposes to call clasolites. 



Very little information is given with respect to the rocks of the Molvoke 

 formation other than that contained in pre^'ious papers. 



The Marquette and Ishpeming serpentines are believed to be proved 

 the youngest of the large intrusive masses in the district, and to be 

 younger than any of the dike .rocks except the youngest diabases and the 

 melaphyrs. 



Under the heading of chemical dei)osits the author ])laces the soft iron 

 ores of the district and the quartz veins, some of which can-\- auriferous 

 pyrite and native gold. 



Chapter IX of the i-eport contains a description and an analysis 

 of a new fibrous mineral from the Champion mine, which A. C. Lane 



