1888.] 493 [Crosby. 



tose rocks, but are quite independent of it in the quartzites and 

 other massive varieties. They lack, in a large measure, the 

 swelling or lenticular form of the veins in the western series. The 

 dip of the strata of the eastern series is always high, 70° to 90°, 

 and usually westerly. 



It is not practicable, with the data now at hand, to determine 

 even approximately, the extent of the plication, or the thickness, 

 of either the eastern or western series. Newton has shown that 

 the quartzites of the eastern series are found chiefly in two belts 

 along its eastern and western margins, an arrangement which sug- 

 gests a single gigantic fold. This structure would, however, give 

 the series an almost incredible thickness. 



The preceding descriptions of the Archaean or metamorphic 

 groups are condensed, sometimes without change of language, from 

 Newton's more complete account, which, so far as the writer's ob- 

 servations extend, is substantially accurate, except that he entirely 

 overlooked the conglomerates of the eastern series. This omission 

 is the more difficult to understand, since the conglomerate is a very 

 prominent rock in several parts of the Hills, and since it is certain 

 that Newton examined the ridges on Box Elder Creek and else- 

 where in which it has its best development. I can only conjecture 

 that, in consequence of the extreme metamorphism of the conglom- 

 erate, he failed to recognize its true nature, missing, perhaps, the 

 ledges in which the conglomerate structure is most plainly exhib- 

 ited. Among the localities affording the finest exposures of the 

 conglomerate are the hills above the village of Laflin ; and the ridge 

 on the north side of the road to Galena, about two miles from Laf- 

 lin. This ridge, which is on Box Elder Creek, is probably the one 

 designated by Newton as affording exceptionally fine exposures of 

 the ferruginous strata. 



Although the granitic rocks of the western or older series do 

 not penetrate the newer series, the latter is not probably devoid of 

 eruptive masses. In various parts, but particularly along the mid- 

 dle of the area occupied by the eastern series, there are numerous 

 beds or masses of a dark colored crystalline rock which appears to 

 be chiefly composed of plagioclase feldspar and hornblende and 

 has been provisionally called diorite. So far as observed, the 

 masses of this rock are parallel with the bedding of the schists and 

 slates. But although they are also often distinctly schistose or 

 fissile, they are usually as massive and devoid of bedding lines as 



