JrUSEUM OF COMPARATIVE ZOOLOGY. 117 



decomposed feldspar and hornblende, holding much secondary quartz. 

 The quartz is arranged in the feldspar in the graphic or eozoiin form, 

 which malies the decomposed feldspar a most beautiful object in polarized 

 light. The contrast between the brilliantly polarizing quartz and the 

 feebly polarizing, kaoliuized feldspar substance is thus strongly brought 

 out. The quartz appears to have been deposited from the decomposed 

 feldspar itself, which breaks up into silica and the kaolin-like material. 

 The quartz contains full fluid cavities, those with bubbles, and vapor 

 cavities. The hornblende is in the usual reddish-brown decomposed 

 masses. Some magnetite was seen. This rock is most probably a de- 

 composed old trachyte, although it would doubtless be regarded as a 

 granite poi'phyry by most lithologists. No. 515 is a similar but more 

 feldspathic rock. No. 513 is similar to No. 527, and Nos. 514 and 516 

 are like No. 524. Many pebbles or lenticular masses of clay were seen, 

 that are apparently decomposed pebbles of the conglomerate. 



In the sandstone quarry at the head of the incline on the Hecla and 

 Torch Lake Railroad, the sandstone layers have been regarded as being 

 nearly horizontal. The joint planes that form the floors of the quarry 

 are nearly so, having only a slight dip to the northwest ; but these joint 

 planes cannot be the bedding planes, for we find on close examination 

 that numerous layers of coarser material, pebbles, clay masses, etc. occur 

 in the rock. These layers extend for long distances through the sand- 

 stone, and are always parallel, having the same dip, which is N. 45° 

 W. 15°. These of course, from their character and regularity, must 

 mark the old planes of bedding, while the generally supposed bedding 

 planes are secondary joint planes cutting the bedding planes at a small 

 angle. Tliis sandstone (456, 457, 458, 459, 461, 462, 463, 464) has 

 been leached and acted upon by water the same as that below the Doug- 

 lass Houghton Falls, and its feldspathic material converted into clay or 

 entirely removed. Part of the materials composing the sandstone, espe- 

 cially in the coarser portions, are similar to those in the sandstone at 

 Marquette. The quartz grains are partly water-worn, but a large pro- 

 portion are seen to be short crystals formed of the hexagonal prism, 

 terminated on both ends hy the pyramid, or the usual form found in the 

 acidic porphyritic rocks. It appears, then, as the facets of these crys- 

 tals are comparatively unworn, that they were derived from the destruc- 

 tion or decomposition of trachytic and rhyolitic rocks (granitic and 

 quartz porphyries), the feldspathic material having been removed since 

 by water, leaving a quartzose sandstone. It is a question worthy of 

 examination whether any other sandstones have been formed from 



