262 Dr. F. H. Hatch—The Wicklow Greenstones. 
In the notes appended to the memoir referred to above, the 
greenstones there described are arranged in the following cate- 
gories :—a. Quartz - mica -diorite; 6. Quartz -diorite and diorite ; 
c. Augite-diorite; d. Dolerite (diabase) ; e. Epidiorite (passing into 
hornblende-schist) ; and f. Serpentine. 
(a) Quartz-mica-diorite (the Tonalite of vom Rath).—A fine 
example of this rock occurs as an irregular boss, extending from 
Carrigmore to Westaston, 4 miles HE. of Rathdrum (Sheet 1380). 
The central portion of the mass is traversed by the road going from 
Rathdrum to Kilboy Bridge. The rock is remarkable for its 
granitoid appearance, the grain being moderately coarse and the 
colour light. Some parts of the mass are spangled over with lustrous 
six-sided plates of dark mica; while in others the mica is replaced 
by chlorite. At Carrigmore the mica occurs in thin bronze-coloured 
films, covering irregular patches of the rock’s surface. Under the 
microscope these patches appear as ophitic plates of a bright reddish 
brown colour. 
The component minerals of the rock are quartz, felspar (mostly 
plagioclase, but with a small quantity of orthoclase), biotite, a pale 
green hornblende, a few grains of colourless augite (malacolite), 
chlorite, and apatite. 
The quartz is abundant. It was evidently the last mineral to 
separate, since it fills the interspaces between the idiomorphic 
crystals of the earlier-formed minerals. Apatite is also present in 
considerable quantity ; and its six-sided acicular microlites are found 
penetrating all the remaining minerals. The chlorite has resulted 
from the alteration of the mica, the plates of which are sometimes 
surrounded by a border of chlorite, sometimes altered almost com- 
pletely into that mineral. 
(6) Quartz-diorite and diorite—An excellent example of quartz- 
- diorite occurs at Bologh Lower, three miles E. of Rathdrum. The 
rock is a medium-grained granitic aggregate mainly of felspar and 
quartz, but with some green hornblende and chlorite. Both mono- 
clinic and triclinic felspar are present, the former being fresher 
than the latter. 
The interspaces between the felspar-crystals are filled by clear 
quartz. Green hornblende occurs, sometimes in idiomorphic erystals 
that are evidently original, sometimes in granules and needles, 
imbedded in patches of chlorite, and then perhaps of secondary origin. 
In structure and composition the rock much resembles a horn- 
blende-granitite ; but mode of occurrence and association show that 
it belongs to the greenstone rather than the granite family. 
Similar rocks, but with less abundant quartz, occur near Cummer 
Place, six miles E. of Shillelagh. These-are true diorites. 
In all of them the effects of dynamic metamorphism are occasion- 
ally met with, in the shape of finely-granulated patches — the 
so-called “ quartz-felspar-mosaic” — resulting from a molecular 
rearrangement of the original felspar. ‘ 
(c.) Augite-diorite—This type is very common among the 
Wicklow greenstones. It consists essentially of plagioclase felspar 
