78 THE PENOKEE I ROi^ BEARING SERIES. 



wacke, the quartz fragments of these several rocks being shown to have 

 received secondary enhxrgements in optical contiguity with the original 

 grains, subsequently to the aggregation of the rocks. Since the publica- 

 tion of this pamphlet, which was the tirst annovincement of the existence 

 of this very general and wides])read mode of induration of rocks, our 

 experience has only confirmed the conclusions presented, showing us not 

 only these enlargements are to be widely met with in the Penokee district, 

 but more than that, that quartzite fragmental rocks of all ages are found 

 to be much more rarely without these enlargements than with them. 



1885. 



WiNCHELL (N. H.). The Crystalline Rocks of the Northwest. Address before 

 Section E., Am. Assoc. Adv. Sci., at Philadelphia, September, 1884^. Proceediugs, 

 33d Meetiug, pp. 3(i0-379. 



In this address Prof Winchell "calls the attention of Section E to 

 some of the interesting problems that beset the geologist who undertakes 

 to study the crystalline rocks of the Northwest, and especially that part of 

 the Northwest which is included in the state of Minnesota," and aims at a 

 concise review of "the broad stratigraphic distinctions of the crystalline 

 rocks that have lately been studied in Michigan, Wisconsin, and Minnesota 

 by the aid of the published results of the surveys of Brooks, Wright, 

 Irving, Rominger, Pumpelly, and others," who undertook to formulate a 

 generalized statement. To this he adds also "such published results and 

 unpublished field observations from Minnesota as may be furnished by the 

 survey of that state, in order that the scheme may cover coiTectly the 

 crystalline rocks of the entire Northwest." 



The following table indicates the six groups into which Prof Winchell 

 would divide all of the rocks of the Northwest which belong below the 

 Copper-bearing series: 



