172 
Mr. Weaver on the 
§ 63. In Croghan Kinshda (See PI. 8. No. 7, PI. 10. No. 18, 
and PI. 7. No. 3.) granite supports clay slate ; and so me thousand 
fathoms of trenches having been cut down to the solid rock in 
quest of auriferous veins, the mineral structure of this mountain 
was gradually and fully disclosed. The western arm and brow of 
the mountain consist wholly of granite; and in the trench cut 
along the northern brow of this arm, I observed and measured the 
following succession and alternation of rocks proceeding eastward 
across the line of their direction. 
No. fathoms 
1. The fundamental granite. This is traversed at the place now des- 
cribed by a vein of quartz about two feet wide, containing cavi- 
ties lined with quartz crystals. The rock itself is small grained, 
composed of yellowish or greyish white crystalline felspar, grey 
vitreous quartz, and blackish green mica : the felspar predomi- 
nating and the mica being in the smallest proportion. 
At the distance of 53 fathoms from this vein is another, four 
feet wide, composed of white quartz with a greasy lustre and 
greenish grey clay slate ; beyond which the granite extends forty- 
five fathoms farther. 
2. Then greenish grey clay slate for 8 
3 . Granite and some clay slate 11 
4. Greenish grey clay slate 149 
5. Granite 16 
6. Clay slate and granite in repeated alternations, the clay slate some- 
times containing large grains of translucent quartz, and occa- 
sionally also a few crystals of glassy felspar. These alternations 
form a thickness of 32 
7. Granite » 160 
8. Greenish grey clay slate 15 
9. Granite 21 
The predominant part of this rock and of No. 7, is greyish white 
felspar, with grey quartz, intermingled with spots of blackish 
green mica. The grain is small, and the rock sometimes much 
resembles the fine grained granite in the greywacke slate of 
Windmill hill, already described, (§ 54.) 
