148 
Mr. Weaver on the 
thickness, was thus completely altered throughout its substance, 
appearing of a bright pinchbeck hue. Some of the hornblende rock 
has much pyrites disseminated through its substance. These masses 
look like the wasted remains of a great bed protruding from the 
mica slate ; but certainly not forming a continuous bed of any con- 
siderable extent, for they do not appear either on the Glenasane or 
on the Glendalough side of Comaderry. Two blocks of hornblende 
rock may be observed by the road side, leading to Glendalough, 
from the Seven Churches, which are probably detached portions 
from the same bed. 
§ 31. In the precipices of Glendalough, the mica slate exhibits 
frequent beds of quartz, which seldom exceed three feet in thick- 
ness : and in the vicinity of the granite, it is not unfrequently tra- 
versed by numerous contemporaneous veins of quartz ; but neither 
here nor in Glenasane, is there any appearance of alternation with 
granite. In Glenmalur, however, the case is very different, nearly 
one half of Lugduff, which borders the glen on its north side, being 
composed of these alternations, the study of which has in this place 
been greatly facilitated both by nature and art ; the northern face 
of Glenmalur being furrowed by several ravines, and the lead mine 
of Ballinafinchogue being situated in this quarter. One of the best 
lines afforded for examining the succession of these beds is the ra- 
vine, the water from which turns the wheel of the upper smelting 
house. If we follow this ravine upward, making a rough measure^ 
ment up the inclined face of the mountain, we find, 
1. Granite, at bottom, of uncertain thickness, upon which rests a bed of 
2. Mica slate, that includes, however, many layers of granite, from a few 
to several inches in thickness, which alternate with the mica slate, 
forming a body . . . . 4 fathoms thick 
3. Then granite ....... 2 fathoms 
