GEOLOGICAL EXPLORATIONS AND LITERATURE— 1881. 79 



sandstones, etc., baviuy been laid down in tin- usual way, were tlieii disturbed by the 

 eruption of the jasper and ore; this formed the knobs of jasper, the banding belong- 

 ing to the fluidal structure, and not to sedimentation. Besides occurring in bosses, 

 the jasper was spread out in sheets, and intruded through the roclv in wedge-shaped 

 masses, sheets, and dikes. Much of the original rock still remained horizontal, and 

 new sedimentary deposits continued to be formed out of the jasper and the other 

 rocks. Next came the eruption of "diorites," -which completed most of the local 

 folding and tilting of the strata. Finally, the granite eruption took place on both 

 sides of the •'Ilurouian," uplifting and contorting the strata near it, and perhaps 

 laterally compressing the inclosed iron-bearing rocks. No basis exists so far, then, 

 for the scheme of formations laid down by Mr. Brooks, as it was founded on the 

 suj)position that all the rocks were sedimentary. 



Although, in deference to the common custom we have employed the term 

 jasper in writing of the siliceous eruptive rocks associated with the ore, in reality it 

 it not properly called so. * * * It is more acid than the rhyolites, the silica being 

 above 80 per cent. * » * We would propose, therefore, that all the acidic 

 eruptive rocks, whose chemical and physical constitution carries them above the 

 rhyolites should be designated as jd.sjiiUtcs, * * * in accordance with a sugges- 

 tion of Professor Whitney. (Pp. 75-76.) 



issi. 



Wadsworth, M. E. On the origin of the iron ores of the Marquette district, 

 Lake Superior. Read March 17, 1880. Proc. Boston Soc. Nat. Hist., Vol. XX, 

 1878-1880, pages 170-479. 



The baudecl ores of the Marquette district, as will be remembered, 

 are regarded as eruptive Ijy Foster and AVhituey and as sedimentary by 

 Kimball. Since 1865 Kimball's notion regarding them had been generally 

 accepted; at any rate it was not seriously questioiied until Wadsworth 

 reopened the discussion as to their origin. 



The author first states that the ores in question do not, except in some 

 few cases, present the characters of vein-stones. The question to be decided 

 is as to whether "the ore and jaspilite were deposited as sediments in situ 

 or are of eruptive origin." 



The grounds upon which their sedimentary origin had been advocated 

 are these: 



(1) Bog-iron ores are forming at the present day. 



(2) On account of the banding or lamination of the ore and jaspilite. 



