102 THE MAEQUETTE lUON-BEAlimG DISTKICT. 



correctness of tlie jjositioii of tliose who Lave heretofore regarded the two series as 

 equivalent. I came away from the Marquette region, indeed, with a good deal of 

 doul)t as to whether some of the greenish schists inchided by Brooks, Rominger, 

 and others within the lower portion of the iron-bearing series, might not really belong 

 with the older gneissic formation. Excluding these schists, the remainder of the 

 series has a distinctly Huronian aspect. Like the latter, it may be described as, in 

 the main, a fragmental slate and quartzite series, including a large proportion of basic 

 eruptives. * » * Besides the quartzites, magnetitic schists, chert-schists, iron ores, 

 limestones, dolomites, clay-slates, mica-slates, and greenstones, which make up the 

 bulk of the Marquette series, a number of other less abundant kinds have been 

 described as occurring. It is among these kinds that the lithological differences 

 between the rocks of this region and those of the typical Huronian area of Lake 

 Huron are found. * * * 



A considerable proportion of these unusual kinds are plainly but the results of 

 metasomatic changes upon the ordinary basic eruptives of the series, find in the list 

 of rocks so produced come, I think, in all ])robability, a number of the so-called 

 hornblende-schists and actinolite-schists. 



These schists had been regarded as sedimentarv h\ tmnw oljservers 

 because of their schistose structure, but to Irving thev seem ;uiquestion- 

 ably eruptive. 



The question as to the successiou of beds in the Marquette district 

 is left unsolved. Neither Brooks's nor Rominger's scheme is accepted, nor 

 is any other one adopted. Tlie greenstone layers, XI, IX, VII, and those 

 below V of Brooks's di\isi()ns, including hornblendic and chloritic schists, 

 are all believed to be erujttive, some contemporaneous with the sedimentary 

 layers, and others intrusive in and between them. 



With respect to the origin of the jasper ores, the author writes (pp. 

 192-103): 



My studies in this connection are as yet incomplete, and I feel unwilling, therefore, 

 to advance any general theory. But several points with regard to these ores which 

 have impressed themselves upon our attention may be mentioned. In the first place, 

 I may say that I am quite unable to accept any of the jasperj' ores as of eruptive 

 origin. From the most highly contorted and confused forms we have every gradation 

 to forms in which the sedimentary lamination seems so distinct as to render irresist- 

 ible the conclusion that all are of one origin. * * * Jaspery and quartzitic ores, 

 which must, I thiuk, be admitted by all to have had the same genesis with those of 

 the Marquette region, occur in the Penokee-Gogebic belt, and again in the Animikie 

 formation of the National boundary, in a relatively undisturbed position arul under 



