56 



BULLETIN OF THE 



ide of iron and quartz. Contrary to the views of Dr. Wichmann and 

 Prof. Zirkcl, we regard these as the products of decomposition of the 

 feldspar and its enclosed foreign materials, and not originally formed 

 products. Likewise we find the same alteration products in distinguisli- 

 able plagioclase as well as in orthoclasc.* The quartz occurring in the 

 feldspar appears to be a secondary product, as also is part of that occur- 

 ring independently in the rock. Many minute microlites occur in the 

 decomposed portion of the feldspar as a secondary product. The quartz 

 contains fluid cavities and microlites. No salt cubes were seen in the 

 fluid inclusions. It will be remembered that Air. Charles E. Wright 

 pointed out that what he supposed to be the younger " Iluronian *' gran- 

 ite contained such cubes in the fluid inclusions, while the *'Laurentian " 

 granite did not. Here we have an eruptive granite in a district mapped 

 as " Huronian " that so far reveals no salt cubes. Of course, the evidence 

 is negative; in another section, or possibly in some overlooked portion 

 of this section, they might be found. So long as Mr. Wright has used 

 this as a means of diagnosis, we point to the results here simply for 

 what they are worth to those who rely upon microscopic analysis only. 

 The hornblende is of a green color, and is broken and torn. Consid- 

 erable magnetite, pyrite, and secondary hematite was seen. Some mi- 

 nute crystals and grains, supposed to be zircons, were also observed, as 

 well as secondary epidote. Titanite is quite abundant. The granitef 

 at the mouth of Dead River (62, G3) is seen microscopically to be simi- 

 lar to the one just described {*^(^). Its feldspar is not so much decom- 

 posed, and the orthoclase and plagioclase are readily distinguishable, 

 the latter being quite abundant. The hornblende has been almost en- 

 tirely altered to chlorite and biotite (1). The quartz contains microlites 



and fluid and vapor cavities. Some minute crystals of zircon were seen 

 in the feldspar as well as in the quartz. The decomposed feldspar is 

 almost filled with microlites. Epidote is abundant as a secondary pro- 

 duct. The rock also contains magnetite. 



Specimen 82 (p. 52) is a pinkish-gray granite. Under the micro- 

 scope it is seen to be composed of orthoclasc, plagioclase, quartz, biotite, 

 muscovite, and magnetite. The feldspar is fresher than in the preced- 

 ing granites, and contains numerous mica inclusions, mostly muscovite. 

 The qnai'tz holds microlites and both glass and stone cavities. The 

 muscovite generally cuts through or is mortised into the biotite, the 

 same as the feldspar is in the augite of the diabases. The musco- 



* Geol. of Wise, III. 601. 



f Cliloritic gneiss of Brooks. Geol. of Wise, HI. 662. 



i 



\ 



^ 



