MUSEUM OF COMPAKATIVE ZOOLOGY. 



57 



vite is quite subordinate to the biotite, and the plagioclase to the 

 orthoclase. The red granite youth of Ishpeming (No. 194, p. 55) is 

 composed of orthochise, pkigioclase, quartz, viridite, magnetite, and 

 hematite. The feldspar is somewhat altered, the plagioclase showing 

 the same microlites and hematite alteration products as the orthoclase. 

 Part of the feldspar shows very beautifidly the polarization characters of 

 microcline. The original mica in the rock is now altered to a viriditic 

 material. The quartz contains inclusions of feldspar, biotite, microlites, 

 magnetite, and fluid, vapor, glass, and stone cavities. The gneiss, in which 

 this last granite is eruptive, is a dark gray foliated rock (192, 193) com- 

 posed of biotite, quartz, orthoclase, plagioclase, -magnetite, and a little 

 pyrite. The feldspar is much decomposed, and contains microlites, 

 as well as the lenticular, colorless foliar, so common in the decomposed 

 feldspars in the granites of this region, which we suppose belong to mus- 

 covite. The quartz contains the same little disks, as well as fluid and 

 vapor cavities. Numerous microlites of apatite, as well as some grains 

 that may belong to zircon, occur in the rock. The characters of the 

 rock appear rather to bo those of an eruptive than of a sedimentary one; 

 but as its relations to anything older than itself were not determined, 

 nothing definite can be said upon this point. In a section made of an 

 intrusion of the granite through the gneiss (195), both show their re- 

 spective characters as given above. 



One half-mile southwest of Huniboldt the granite is intrusive in a 

 mica schist. The granite at this point is white, and not of the usual 

 pinkish color. Southeast of the Old Washington mine the pinkish gran- 

 ite (323) was found intrusive in a hornblendic gneiss. We have termed 

 these rocks granite because the foliation appears to be a fluidal struc- 

 ture parallel to the contact planes, and because they pass into regu- 

 larly non-foliated granites at a distance from their junction with the 

 schists. 



Southeast of the Champion mine the granite (350, 351) is found in- 

 trusive in a schist (349, 352, 353, 354). The schist is indurated and 

 much changed where the intrusive tongues of granite enter it (347). 

 There can be no question that the granite is intrusive, and younger than 

 the schists. They have both been mapped by Mr. Brooks as " Lanren- 

 tian." Four hundred feet east occur his Huronian magnetic schists 

 (348), having exactly the same strike and dip as the schists in contact 

 with the granite. Furthermore, if we could prolong the magnetic 

 schists in the line of their strike, so far as we coidd ascertain, the non- 

 magnetic schists would be included directly in them as a component 



