458 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 11, 



7. Ontonagon District. — The mines of this district are all opened in 

 the same clas& of deposits — namely, very irregularly defined lodes 

 which follow the strike of the trappean belt, commencing on the 

 Minnesota Hills, at the southern end of the district, which rise 

 abruptly from a drift-covered plateau, about 12 miles in length, 

 lying to the south of the town of Ontonagon. They extend in a 

 north-easterly direction for about 16 miles to theWynona mine, the 

 last explorations in the direction of Portage Lake. The Minnesota 

 mine has been worked to a depth of about 200 fathoms, on a lode 

 dipping about 46° northerly, and included between a roof of compact 

 grey trap and a fioor of conglomerate. A northern branch, dipping 

 at a higher angle, falls into it at the fifth level below the adit ; be- 

 tween these is another branch, more nearly parallel with the main 

 lode, in which the great mass of 400 tans was found in the year 

 1856, about 20 fathoms below the surface. This mine has ahown 

 a decided decrease of richness in depth, the produce having diminished 

 from 2058 tons in 1857, derived from ground yielding 1267 lbs. per 

 fathom, to 387| tons in 1864, the amount per fathom being reduced 

 in the latter year to 186 lbs. The lower workings are now com- 

 pletely abandoned, and an attempt is being made to develope the 

 northern lodes. As seen in the adjoining National mine, the Minnesota 

 lode is filled with a mass of epidote and quartz, apparently of a 

 brecciiform structure, with rough particles of copper scattered irre- 

 gularly through it. The hanging waU is full of small slipped pieces 

 o-f rock and clay, and is covered with longitudinal striations. 



The sandstone below the conglomerate on the underside of the- 

 lode occasionally contains a little copper, when it assiimes a lami- 

 nated appearance, in thin stripes of red jasper and yellow epidote 

 grains, interspersed with bright metallic leaflets, the arrangement 

 being similar to the cement of the Albany and Boston conglomerate 

 and the compact epidote-rock of the Porcupine Mountains. 



The lode at the Indian mine is an epidotic mass, apparently a con- 

 cretion in the hornblendietrap. It is remarkable for carrying large 

 quantities of analcime, with small masses of copper in sohd crystals. 

 A very decided concretionary structure is seen in the trap at the 

 Bohemian and Toltee mines, which are on the same run of ground ; 

 the deposit worked is a course of trap, filled with epidote about 8 feet 

 thick, the rock containing spheroidal masses which in section pre- 

 sent alternately light- and dark-green rings, the former being due 

 to epidote, and the latter to the prevalence of hornblende and chlorite, 

 the two colours being divided by intermediate rings of calcspar : the 

 largest of these concretions are about 15 inches in diameter. The 

 lode is an epidotic amygdaloid, about 8 feet in thickness, with a 

 N.W. dip of 35°. It is spotted through with small strings of 

 calcspar and quartz ; the copper occurs either in pseudomorphs or in 

 crystallized masses of no great size, or in leaf -like plates in the bright- 

 green epidote : similar conditions prevail in the Wisconsin mines fur- 

 ther to the N.E. ; but as yet none of these mines are distinguished by 

 any great production. Several heavy masses have recently been taken 

 out of the shallow workings at the Flint-Steel mine, which is opened 



