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BULLETIN OF THE 



No. 524 is a more compact rock of like cbaractei'. Its groundmass is 

 kaolinized and holds the quartz and feldspar alteration products. It 

 is filled with grains and masses of fcrrite probably derived from Lorn- 

 blende. The feldspar is so decomposed that it cannot be told whetlicr 

 it is plagioclase or orthoclase, Nos. 52G and 529 are like No. 523, 

 while No. 530 is more allied to No. 524. 



No. 527 has a more coarsely crystalline, granitoid structure, showing 

 under the lens a reddish and grayish brown groundmass, holding elon- 

 gated brownish-black hornblende crystals. In the thin section it is 

 seen to be composed of feldspar, magnetic iron, horublendo, and some 

 quartz. The feldspar is greatly altered, and is now composed of inter- 

 growths of feldspar and quartz, giving rise in it to a structure resem- 

 bling that of graphic granite, or much of that figured as belonging to 

 the Eozoon Canadcnse. The quartz is all secondary, and the hornblende 

 altered to reddish or yellowish brown ferruginous masses. 



No. 528 is a fine-grained granitoid trachyte (granite porphyry), but 

 in the thin section the feldspar is seen to be so altered and filled in with 

 secondary quartz, containing full and bubble-bearing fluid, and vapor 

 cavities, that the section resembles that obtained from some fragmcntal 

 rocks. No. 525 is a rock of similar character. 



Nos. 538, 539, 541, and 544 are good examples of some of the sand- 

 stones on the river below the melaphyr. No. 538 is seen in the section 

 to be composed of quartz and trachytic detritus. 



Below and at the base of the falls the dip remains the same as before, 

 N. 45° W. 10°, but above tliis locality the inclination varies, rising from 

 15° to 18° between the first and second falls. In some places a qua- 

 quaversal dip was seen. Some five falls exist in the river, and at the 

 last or upper fall the melaphyr was found. The dip of the sandstone 

 has now increased to some 20°, but still dips northwest, and the first 

 trappean flow is seen to overlie and greatly indurate and alter it. This 

 immediately underlying sandstone (537) is filled in with little reticulated 

 veins of calcitc, a! kaolin-like material, etc., and in general resembles tlie 

 baked sandstone found underlying the trap on the western side of Ke- 

 weenaw Point. Microscopically, it is seen to be composed of the debris 

 of the trachytes previously described. This sandstone was seen within 

 three inches of the melaphyr, and although there may have been some 

 eliding motion between the two, as the contact was not seen, yet the 

 induration of the sandstone, its dip, and its relations to the melaphyr, 

 prove that it underlies the latter, which flowed over it. This, then, 

 ■with evidence obtained on the Douglas Houghton Kivcr, settles the 



