54 . BULLETIN OF THE 



from original water-worn grains, but from the Assuring of an originally 

 continuous siliceous mass. The quartz contains fluid cavities, mici*o- 

 lites, and little flakes of mica. !Xo. 128, nearer the Huronian, at the 

 edge of the granite, is microscopically seen to be in finer quartz grains. 

 This rock also contains greenish mica, clusters of actinolite crystals, and 

 garnet grains. The quartz grains contained the same inclusions as 

 those in No. 129. Some magnetite was observed. The actinolite crys- 

 tals were often seen to extend through two or more of the adjacent 

 quartz grains, not having been broken by the process of fissui'ing the 

 quartz. 



Specimen 130 consists of two pai-ts, — the schist already described, 

 and the granite to which it is welded. This granite is here composed 

 of quartz, biotite, and grains of garnet. The quartz is in the same fis- 

 sured grains as that in Nos. 128 and 129, and contains microlites, minute 

 crystals of greenish mica, and fluid cavities. The majority of the fluid 

 inclusions lie in the secondary fissures, but part are in the solid quartz. 

 The biotite is seen to frequently extend from one quartz grain into an- 

 other without having been broken by the Assuring of the quartz. The 

 garnet contains actinolite crystals, and the same black grains that it 

 did in the adjacent schist (130). The biotite and garnet ai-e evidently 

 derived from this schist, and are in fragments. This section, more 

 than either No. 128 or 129, shows the eflect of the schist in adding 

 foreign ingredients to the granite, and also the action of the granite on 

 the schist by tearing off and dissolving portions of its material. Such 

 phenomena are the usual accompaniments of the mutual reaction of 

 two rocks when one is intruded through the other. The three sections 

 128, 129, and 130 well illustrate the diff'erences that can be observed in 

 the same rock within a distance of a few feet. 



It seems appropriate to describe with the granites last given the 

 "quartzite " (page 34) of Mr. Brooks at Republic Mountain. The rock 

 (95, 115, 116, 117, 118, 119) is greenish gray, macroscopically containing 

 quartz, actinolite, and epidote. Under the microscope it (115, 118) is 

 seen to contain quartz, actinolite, hornblende, greenish mica, epidote, 

 magnetite, and hematite. The quartz is in similar grains to that in 

 Nos. 128 and 129, and contains numerous microlites and mica inclu- 

 sions, as well as fluid cavities. This rock, it would seem, belongs to the 

 granites adjacent to Republic Mountain, and is an ofl'shoot from them. 

 In microscopic characters they are closely allied, but we only offer this 

 for what such characters are worth in such questions as these. One thing 

 we know. This (" quartzite ") granite is eruptive in its present place, 



