140 
Mr. Weaver on the 
2. Mica Slate . 
§ 21. The mica slate, wherever it occurs, is in direct contact with 
granite, whether situate on the eastern or on the western side of the 
granite region. I shall first consider the eastern division, following 
throughout its line of junction with the granite, the most northern 
extremity of which is to be found in Killiney bay, and the most 
southern in the barony of Shillelagh, in the county of Wicklow. 
In the former, the mica slate leans against, and is supported by a base 
of granite on the south-eastern side of Dalkey-hill, below the obelisk. 
It occupies the coast for about 300 yards, ranging north-east and 
south-west, and dipping 80° south-east; and at its northern ex- 
tremity granite may be seen as a sort of pediment beneath it. This 
mica slate consists of alternate layers of quartz and mica, from one 
line to two and three inches thick ; and some layers of quartz extend 
even to two feet in thickness, while the surface of the intervening 
mica is almost invariably thickly studded with cruciform and stelli- 
form aggregations of hollow spar. 
South of this rock, the coast is covered by a great accumulated 
mass of rubble and soil, and after an interval, the granite rock re- 
appears, some of it being very large grained ; projecting in the 
southern part toward the sea; and on the eastern side of this projec- 
tion is applied a thin mass of mica slate. To the south of this point, 
rubble and soil again occur, forming a depth of one hundred to one 
hundred and fifty feet. This accumulation, however, probably rests 
upon mica slate, for this rock comes forth to the day higher up on 
the eastern side of Rochetown road, where it supports the upper 
Martello tower, ranging 15° north of east and south of west, and 
dipping 40° toward the east of south. 
