144 THE REV. MAXWELL H. CLOosE, 
It is, of course, quite possible that there may be friction slicken- 
sides on planes of dislocation in the granite. There must have 
been such planes produced during the disturbances after the Car- 
boniferous age, when the granite had been thoroughly solidified, 
and great friction must have taken place along them; but the 
slickensides so frequently to be seen in the granite joints of this 
neighbourhood are, at least as a general rule, most clearly struc- 
tural and not the result of friction. The slickenside striations of 
the quartz coating of a joint surface are often accompanied by ca- 
pillary schorl, the needles or tibres of which are accurately 
parallel to the slickenside striation and unquestionably form part 
of the phenomenon. The great majority of the slickenside-bear- 
ing joints of a neighbourhood have a very observable nearness of 
direction with each other; the mean dip of these surfaces is at 
about 80°, so that the variation in the direction of the planes is 
only one half that of the strikes of the planes. Moreover, the 
striations are not only strictly parallel on the same surface, but 
they very seldom deviate much from the mean direction in their 
vicinity ; showing that their directions have been influenced by 
some common cause. This can be well seen in many places; of 
which one of the most easily indicated and accessible is the shore 
at Sandycove (between Kingstown and Dalkey), from the bottom 
of Burdett Avenue for some distance eastwards. 
The granite is often penetrated by dykes and veins of eurite 
(which may be called a fine close-grained granite with very little 
or no mica) and by veins of quartz. These, when they intersect 
can often be seen to be of different ages; and they are sometimes 
faulted. The eurite veins may be intrusions of later date than the 
solidification of the surrounding mass, or they may be only infil- 
trations into contraction fissures; the quartz veins have been 
doubtless formed by infiltration. 
Occasionally, though apparently very rarely, the granite in 
this neighbourhood exhibits an obscure concretionary structure. 
Sometimes a freshly exposed joint surface will show indistinct 
concentric rings of colour two or three feet in diameter, usually 
iron staining, which might, at first sight, lead to the supposition 
that the joint had cut across a concretionary spheroid ; but it 
will usually be manifest on closer inspection that the phenomenon 
is confined to the joint itself. In some places, as near Mur- 
