ARCH^AN GROUP. 271 



down the valley, a good exposure, of which a part is given below, occurs in 

 the northwest strike. This outcrop is affected seriously by a later fault. 



Dip from 50 degrees (on west) to 73 degrees (on Arrott's Branch), south 54 

 degrees west. Beginning above — 



1. Brittle white quartz in thick bands and dikes. 



2. Euritic granite, pink-brown gneissoid, intrusive in amphibolitic schists. 



3. Continuation of schists, with bands of 



4. Friable brown gneiss, gradually becoming tough. 



5. Tough blue indurated shale, or slate, thinly fissile. . 



6. Chloritic schist (prochlorite? G-= 2.963). 



7. Altered schist (G-=2.94), chloritic?. 



8. Blue marble, part coarsely crystalline calcite; part compact, streaked blue marble 

 (Gr= 2.692), part crystalline-granular dolomite. 



SECTION C 



In the upper course of Johnson Creek, northwest of Valley Spring, Llano 

 County, at a mound known as ''Iron Mountain," the following incomplete 

 section is afforded. This is not badly confused, but as in many other places 

 a portion of it is covered by wash from the later terranes. In this instance 

 the upper part of the section is obscured, but exposures farther to the south- 

 east lap over in such a manner as to give the proper connection. 



Beginning upon the southwest with nearly vertical strata, dipping south 

 54 degrees west, the rocks appearing beyond the wide area covered by detri- 

 tus, are — 



1. A granite or mica schist series, in part rotten and highly micaceeus, with included 

 bands of porphyritic granite intrusions?, the whole representing apparently a horizon be- 

 low Nos. 1 to 4 in Section A. These are followed below by 



2. A thick deposit, in strike, of very pure magnetite, with hematite shading very gradu- 

 ally below into quartzose magnetic schist; in all 50 feet to 60 feet. 



3. A band of binary granite (altered) carrying much magnetite and a green phosphatic 

 mineral (glauconitic apatite), below which is 



4. Fine-grained sandrock (brownish), with scattered grains of magnetite. 



Then follows, in the anticlinal areas and beyond, upon a steep north 54 de- 

 grees east dip, a great thickness of 



5. Granular, micaceous, schistose rocks, somewhat like the latest (Bodeville) series of 

 the Burnetan System, but more friable and less crystalline, with bands of fine-grained 

 quartzite. 



Southeastward, in the continuation of this strike, which crosses the Llano 

 River 4 miles west of Llano City, this section is in part repeated, and its ex- 

 tension upwards may be denned as follows, viz. : 



6. Magnetite and congeners, similar to Nos. 1 to 4, in reverse order, overlaid by 



7. Graphitic schists, followed by 



8. Slates and schists, tough, more or less chloritic; overlaid by 



9. Crystalline dolomitic marbles. 



