V 



on the Lake Superior Land District 235 



It is of a buff color — in some places silicious^ with quartzose 

 nodules ; but in otherSj highly rnagnesian, containing about 45 

 per cent, of carbonate of magnesia. 



From the horizontality of the first described deposit, which 

 occurs about a quarter of a mile to the north, it seems evident 

 that the limestone overlies the sandstone, although the position 

 of the inclined beds of the more southerly portion of the lime- 

 stone is at first difficult to explain, since the surrounding country 

 is low and level, and underlaid by sandstone in horizontal beds- 

 It seems evident that at this point the country has been disturbed 

 and upheaved by igneous action beneath, which has raised the 

 strata, without any appearance of trappean rocks on the surface- 

 rhis view of the case is corroborated by the fact that at no great 

 r distance from this point an elevation occurs from which the strata 



\ of sandstone dip on all sides, and although there is no igneous 



rock visible, yet it is evident that the sandstone has been raised 

 in a dome-like protuberance by a mass of igneous rock pressing 

 upon it from below. The same cause is also indicated by the 

 irregular variation of the magnetic needle in the vicinity observed 

 hy the linear surveyors, which is unusual except when caused by 

 the proximity of the trappean rocks. 



The isolated knob of trap called Silver mountain, which has 

 been before described, is an example in point — where, however, 

 the elevating force has not only been sufficient to raise and shat- 

 ter the strata of sandstone, but, at the same time, to protrude a 

 ttiass of molten igneous matter above the surface. 



Geological Position. — As to the geological position of this 

 limestone, there can be little doubt that it is superior to the sand- 

 stone. Mr. Whitney and Mr. Hill have both explored it with 

 care, and both have arrived at the same conclusion. The sand- 

 stone, wherever observed in this region, rests unconformably on 

 the argillaceous schists. It is seen in this position ten miles 

 east of this deposit, and is found in the beds of the streams in 

 this vicinity. On the southern side of the axis, Messrs. Foster 

 and Hill found these two groups occupying the same relative 

 position." 



The point is one of great interest to American geology, and 

 ^vill not be permitted to rest until the facts are too clearly made 

 out to admit of farther discussion. 



^ In the chapters on Mines and Mining, much valuable informa- 

 tion is condensed which will be found practically useful. The 

 following paragraphs present some interesting facts respecting the 

 nietallic veins of the region. 



"The materials composing the ganguo of veins are often ar- 

 ranged in parallel plates, constituting what the Cornish miners 

 <^all comby lodes. De la Beche supposes that this arrangement 

 resulted from successive openings of the fissure. 



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