1867.] MACFARLANE — GEOLOGY OF LAKE SUPERIOR. 199 



the greenstone its schistose structure. The other facts, described 

 above as observable at a considerable distance east of Eagle River, 

 shew that something more than a mere modification of form is 

 caused by the action of basic greenstone upon granite fragments. 

 Not only are the latter there observed to be enclosed in, softened by, 

 and twisted around with the greenstone, but the phenomena observ- 

 ed fully justify the supposition that they have been dissolved in 

 it, that is to say, actually fused in and incorporated with its ma- 

 terial. The fragments are seen to be firmly joined together with 

 the enclosing rock, especially where the latter becomes more 

 siliceous. Furthermore, their sharp angles are often rounded off, 

 indicating plainly that these parts were first melted away by the 

 fluid greenstone. Moreover, the product of the union of the latter 

 with the dissolved parts of the granite is plainly visible. It is the 

 siliceous slate rock described above as forming in places the matrix 

 of the breccia. This siliceous rock, the specific gravity of which 

 is much lower than that of the greenstone, is further seen to be 

 twisted about with the latter in such a manner as, in its turn, to 

 envelope parts of the greenstone, thus shewing that motion assisted 

 the incorporation of the two. The reddish grey felsitic rock, 

 mentioned as occurring at the junction of the two formations in 

 the north-east corner of Bachewahnung Bay, has doubtless had a 

 similar origin to fat of this siliceous rock, and it is not unlikely 

 that the banded traps and slates, so frequently found among 

 Huronian rocks, are attributable to a similar mode of formation. 

 Closely connected with the breccias just alluded to, so far as re- 

 gards the cause of its peculiar structure, is the Huronian slate 

 conglomerate. It is impossible to examine closely this rock with- 

 out being impelled to the conclusion that its origin is not very 

 different from that of the breccias ; that its matrix has been a 

 fused mass, flowing slowly but constantly in the one direction ; 

 and that its boulders are merely fragments which have been half 

 melted and rounded off by contact with the igneous rock. The 

 oval, twisted, lenticular and long drawn forms of the boulders are 

 such as could never have been produced by ordinary attrition, and 

 they frequently furnish examples of such intimate amalgamation 

 with the matrix as are never found in aqueous conglomerates. 

 Further, the fact of the boulders being frequently drawn out into 

 what are simply bands of light coloured slate, not only disproves 

 the sedimentary origin of the conglomerate, but indicates the 

 manner in which the association of greenstone slate and siliceous slate 



