MUSEUM OF COMrAR.VTIVE ZOULOGY. 19 



bear, and cracks or breaks, and faults or throws, are the result, though 

 these are not numerous in the Lake Superior region. Cracks so pro- 

 duced, and filled with material other than that constituting the adjacent 

 rocks, are called dykes ; or, if the material be crN-stalline and metallif- 

 erous, veins. As iron ore in workable quantities does not occur in this 

 form in this region, vein phenomena will not be considered here." Of 

 the Huronian series " the prevailing rock is a greenstone, or diorite, in 

 which, like the copper traps, the bedding is usually obscure ; but the 

 intercalated schists and slates, which usually bear strong marks of strati- 

 fication, make it usually not difficult to determine the dip of the beds 

 at any point. . . . Descending to the oldest or bottom rocks of the 

 Lake Superior country, the granites and associated beds {Laurentian), 

 we find the bedding indications still more obscure, and often entirely 

 wanting." {I. c, pp. 74, 75, 76.) 



" In subdividing the Huronian or iron-bearing series which we have 

 particularly to study, the rocks have been grouped (1) lii/iolor/icalli/, i. e., 

 according to their mineral composition, and (2) stratirj rajihicalhj, i. e., ac- 

 cording to relative age. As this system was first described and named 

 by the Canadian geologists, their names have been employed as far as pos- 

 sible in the body of this report ; the identity in composition of many of 

 our I'ocks with theirs, having been established by an examination of a large 

 number of Marquette specimens by Dr. T. Sterr}' Hunt." (/. c, p. 82.) 

 " The several beds or layers of the Huronian system, as developed in the 



Marquette region, are numbered upwards from L to XIX I., IT., 



III., IV., are composed of beds of siliceous ferruginous schist, alternating 

 with chloritic schists and diorites, the relations of which have not been 

 fully made out ; Y. is a quartzite, sometimes containing marble and 

 beds of argillite and novaculite ; VI., VIII. and X. are siliceous fer- 

 ruginous schists ; VII., IX. and XL are dioritic rocks, varying much 

 in character ; XIII. is the bed which contains all the rich specular and 

 magnetic ore, associated with mixed ore and magnesian schist ; XIV. is 

 a quartzite, often conglomeritic ; XV. is argillite or clay slate ; XVI. is 

 uncertain, it contains some soft hematite ; XVII. is anthophyllitic schist, 

 containing iron and manganese ; XVIII. is doubtful ; XIX. is mica 

 schist, containing staurolite, andalusite, and garnets. This classifica- 

 tion, it will be borne in mind, applies only to the Marquette region. 

 .... These beds appear to be metamorphosed sedimentary strata, having 

 many folds or corrugations, thereby forming in the Marquette region an 



irregular trough or basin While some of the beds present litho- 



logical characters so constant, that they can be identified wherever seen, 



