Dr. F. H. Hatch—The Wicklow Greenstones. 263 
and a pale variety of augite (salite or malacolite). Interstitial 
quartz is sometimes present; and there is a complete absence of 
ophitic structure, the augite occurring in isolated and often well- 
contoured crystals: both, points of distinction from dolerite. The 
felspar occurs in crystals giving lath-shaped sections and exhibiting 
the twin-striation characteristic of plagioclase. It is sometimes 
enveloped by patches of clear quartz, somewhat in the same way 
that felspar-lathes are enveloped by augite in the dolerites. 
Rocks of this character occur abundantly in the neighbourhood of 
Kilpatrick House, N. of Arklow. The exact localities are given 
in the memoir. 
(d.) Dolerite (diabase of the Germans).—The rocks considered 
under this head are composed essentially of plagioclase and augite, 
with a well-marked ophitic structure. The Wicklow type is entirely 
free from olivine, and passes by the addition of quartz, accompanied 
by a change in the nature and structure of the augite, into augite- 
diorite, to which it is naturally closely allied. 
The best representatives of this group occur in the neighbourhood 
of Arklow Head, where they are quarried for road-metal by Mr. 
Parnell. 
The dolerites pass readily into epidiorite; and even when the rock, 
examined under the microscope, appears, at first sight, to be quite 
unaltered, a narrow zone of secondary hornblende will, on nearer 
examination, sometimes be found fringing the augite-patches. But 
the more detailed discussion of these changes is reserved for the next 
section. . 
(e.) Epidiorite.—The rocks embraced under this head are dolerites 
that have undergone alteration under the influence of dynamic meta- 
morphism. Originally they were plagioclase-augite rocks; but, as a 
result of the metamorphism, the augite has been more or less com- 
pletely converted to hornblende. This mineral occurs in ragged 
patches, which in most cases still present the ophitic structure of the 
augite which it has replaced. Other new-formed minerals are chlorite, 
epidote, leucoxene, sphene and calcite. The leucoxene often presents 
elongated streaky forms, suggesting linear extension. Further 
evidence of mechanical metamorphism is to be found in the cata- 
clastic structure frequently presented by the felspar; in such cases 
the mineral loses its homogeneity and appears as a minutely 
granular mass, giving aggregate-polarization (‘felspar-quariz- 
mosaic”). In places where the movements have been great, the 
rock assumes a highly schistose character, and in such places a con- 
siderable proportion of the hornblende is often replaced by chlorite. 
All degrees in the mechanical metamorphism of a greenstone can 
be well studied in the Aughrim Valley, between Woodenbridge and 
Coatsbridge (Sheet 139). The altered rocks occur here in sheets, 
intercalated between the Lower Silurian beds, and are correctly 
represented on the Survey Map as a series of lenticular bands, 
striking N.E. and S.W. At the time when this ground was 
surveyed, however, the effects of dynamic metamorphism had not 
yet been recognized, consequently the schistose character of these 
