On the Physical Geology of the Neighbourhood of Dublin. 141 
that we find the width of the granite exposure to be greatest. 
All these facts point to the conclusion that the granite protrusion 
may not have broken through the thick mass of Silurian strata, 
and that it was brought to the surface by the subsequent 
denudation, which has wrought parts of it into low ground as 
about Kingstown, Carlow, St. Mullins, &e. 
The granite, as already observed, has metamorphosed the 
Lower Silurian slates, all along the line of its contact with them, 
into regular mica schist ; the alteration extends from the surface 
of the granite through a thickness of several hundred feet and 
dies away gradually. The grit bands in the slates are, as might 
have been expected, but little changed. The width of the 
metamorphosed rock, as measured on the surface of the ground, 
is greater on the east, than on the west side of the granite ; which 
seems to indicate that the bounding surface of the granite 
descends less steeply beneath the slates on its east, than on its 
west, side. There seems to be some connection between this 
fact ard that already alluded to, viz., that the small outbursts of 
granite are on the east and that there are none in the Silurian 
on the west side of the main granite exposure. 
The contact of the granite with the Silurian rocks is strikingly 
exhibited on the shore of Killiney Bay, at the base of Killiney 
Hill. Itis there seen that the granite has irregularly penetrated 
the Silurian slates and sent off veins into them; it has also 
caught up what are clearly separated masses of the slate rock, 
converting all into mica schist and developing therein stellate 
crystals of chiastolite. Not far off, on the south side of Roches- 
town Hill, N. and N.W. of Killiney Park, the granite has 
forced several narrow tongues into the slates, nearly along 
the direction of the bedding (see the plan of this in the 
Geological Survey “ Explanations,’ 112, p. 35). 
The Rathmichael relief tank of the Dublin waterworks, on 
the northern hip of Shankill, was excavated directly on the 
boundary line of the 4wo formations. The boundary was dis- 
tinct; but not so much so as at Killiney; and there was a 
peculiar lumpy, lenticular-nodular structure common to the rocks 
on each side of the boundary; the greatest extension of the flake 
lumps being parallel to the surface of separation. At the south- 
ward end of the Scalp—a remarkable physical feature to be men- 
