THE GNEISS AND LIMESTONE. 357 



six miles above its mouth, along the road which follows down the east 

 bank and alongside of which for several miles cliffs of grayish and 

 reddish-gray gneiss extend. 



The limestone does not appear on the east bank of the river, but the 

 directly underlying rusty gneiss forms the upper member of the section 

 here exposed, the calcareous portion showing in small ledges on the west 

 side not far away. The series of gneisses have a general strike of N. 20° E. 

 magnetic, the variation being about 12° west, and the dip is to the north- 

 west at angles of 65° to 80°. The section is exposed for over two miles 

 across the strike, as seen along the road, and in this distance no limestone 

 appears, but in the southern extremity of the section, about two miles in 

 rear of Calumet station, it shows in low-lying ledges near the top of the 

 high hill at this place. Supposing that there is no break in this section, 

 there would be at this place not far from 10,000 feet of continuous 

 reddish and reddish-gray gneisses beneath the limestone. It is evident 

 that such figures, however, cannot be taken as accurately stating the 

 real thickness at this point, as faults and repetitions of strata may occur 

 at several places. 



Their stratigraphic Relation. — The rocks underlying the limestone in 

 descending order, for we now assume the calcareous portion to form the 

 summit of the Laurentian sedimentary and mctamorphic series, may 

 be thus stated : 



Limestone in thin hands with interlaminations of rusty and grayish 

 gneiss, the bands of limestone having a thickness from a few inches to 

 several feet, the gneiss sometimes with a thickness of ten to fifty feet, 

 shading downward into grayish and blackish gray, often garnetiferous 

 gneiss, with certain portions of a reddish shade from the presence of red 

 orthoclase. With these are often associated, more particularly in the 

 upper part, beds of quartz rock or quartzite, which sometimes reaches a 

 thickness of several hundred feet. The above are all found to be well 

 stratified. 



Reddish-gray gneiss, with the indications of stratification less easily 

 seen and in places with foliation only. This underlies the well-banded 

 gneiss of the upper part of the section, and in certain portions even the 

 foliation becomes so obscure as to be indistinguishable except in large 

 well-weathered masses. 



Their physical Characteristics. — The limestone portion in its lowest part 

 has numerous inclusions of the rusty gneiss, which have apparently 

 been drawn out and twisted into long serpent-like forms, sometimes 

 in bands of ten to fifteen feet in length; in other cases the inclusions 

 are small and have more the appearance of pebbles. The limestone 

 itself is frequently intensely crumpled, sometimes in minute crinklings; 



LIII— Bull. Geol. Soc. Am., Vol. 4, 18'J'J. 



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