62 Diorites and Granites of Swift's Creek, 



a. Massive crystalline granular quartz diorites, with some 

 magnesia mica. 



b. Similar rocks, but with fine-grained portions, which are 

 either in contorted foliations of short continuance, or in 

 crystalline granular patches. 



c. Similar to b, but the foliated portions more pro- 

 nounced. 



d. Massive, rather coarse, crystalline granular quartz 

 diorites, as at a. In this is a band of indurated silicious 

 hornfels. The beds are foliated, dipping south at 25°. They 

 are traversed by irregular joints only a few inches apart, 

 dipping north at 75° to 80°. The joints are silicified and 

 very smooth. Silvery mica is deposited on some of the 

 planes of foliation. 



e. Massive quartz diorites, as at a, but having traces of a 

 schistose structure. 



/. Bands of hornfels, as at d, but only about 30 feet across 

 in the whole. 



g. Coarse grey quartz mica diorite, with a gneissic struc- 

 ture. This rock is composed of felspar (microcline, ortho- 

 clase, and a little plagioclase,), magnesia mica, and quartz. 

 The preponderance of triclinic felspars (including microcline) 

 classes this as a diorite. Its structure is that of a gneiss. 



h and j. There are here bands of schistose hornfels. 



k. At this point the diorite-gneiss ceases, and there are 

 thick bands of aplite. An example of the most felspathic 

 variety showed me, when examined microscopically, that it 

 is composed mainly of irregularly-shaped grains of felspar, 

 the greater part of which is orthoclase, the remainder being 

 microcline. Some grains are part monoclinic and part 

 triclinic. There is no plagioclase and not much quartz 

 filling spaces ; nor is there any mica whatever. 



I. The aplite gradually becomes less massive and more 

 schistose, and alternates a little with schists. 



m. Slaty or schistose sedimentary beds, the strike being 

 east and west. These extend to n. 



n. Finely- wrinkled micaceous schist, dipping south at 42°. 



o. Bluish and greenish slates, only slightly micaceous. 



p. Nodular argillaceous schist and micaceous quartz schist. 

 This section crosses the strike of the beds. 



I now give a second example from the Charlotte Spur, at 

 a distance of about 120 chains westward from the last. 



