GEOLOGICAL EXPLORATIONS AND LITEKATaRE— 1881. 85 



the lower luelteil portions of the series, either as dikes or as slieets of a 

 clioritic character. 



The schists coiistiti'iting the greater part of the "dioritic group" are 

 dark-grav or hlackish-greeu rocks, composed of horuljlende, chh^rite, and 

 mica, with feldspar and quartz. Chlorite frequentl}- replaces the horn- 

 blende and often seems to be a product of its decomposition. A part of the 

 schists belonging to the group are composed largely of a hydromicaceous 

 constituent. 



The (lioritie rock-belts are usually imbedded couformably with the schists, and 

 not rarely au insensible gradation from the schistose condition to the massive dioritic 

 can be observed. In the exposures the massive body of diorite generally forms a 

 nucleus around whicli, eccentrically, the inclosing rock masses assume more and more 

 a perfect schistose structure. * * * Other, generally narrower, diorite belts inter- 

 sect the schists transversely, which differ little in composition from the conformably 

 interstratitied masses, ami may, as I previously intimated, represent the lowest, more 

 completely liquefied portions of the rocks in progress of alteration. (P. 24.) 



The schists of this "group" are described as occupying an area south 

 of the northern granite belt, as far west as they Avere examined, viz, the 

 west side of the eastern tier of sections in K. 28 W. On Dead River, 

 above Bancroft's, a succession of schists and diorites, measuring 3,000 feet 

 in aggregate thickness, Avas traversed, but these figures are not regarded a& 

 indicating positively that the thickness of the series is as great as this. 

 There may ]}e folds in the rocks at this point, causing a repetition of the 

 same beds on opposite sides of the axis of folding. They were, however, 

 not detected. 



In its northern portion the schist belt comprises dark rocks with a 

 delicately laminated schistose structure. At Marquette there is interstratified 

 with tliean a belt of Ijanded quartz-schist, which in places becomes a lean 

 magaietite ore. Farther south the schists are lighter-colored and their 

 structure is more fissile and slate-like. Some of the layers are tinged with 

 red oxide of iron, and irregular Ijelts of heraatitic iron ore are interstratified 

 with them,' as at the Harlowe or Eureka mine. Argillite-like beds are met 

 with on the hillside south of Ridge street, in ^larquette, and immediately 

 north of these is a belt of novaculite more than 100 feet in width. South 



