84 REPORT—1857. 
form occurs in the presence of more than one species of Oncoceras, Hall. The British 
specimens have closer septa than those of North America, but are otherwise much 
like. Thus, while there is but one, or perhaps two identical species, the character 
of the fossils is so very similar to that of the lower limestones of America, often con- 
founded (as we learn from Sir W. Logan) in a single calcareous band, that one is 
tempted to conclude that the succession in N.W. Scotland, a thick limestone reposing 
on a quartzite full of fucoidal markings (Nicol, 7. c.), can be nothing else but the equi- 
valent of the calcareous series of Canada, with its underlying Potsdam sandstone. 
On the Junction of the Mica-slates and Granite, Killiney Hill, Dublin. 
By Georcet V. Du Nover, MRA. 
The junction of the mica-slates and granite at Killiney Hill offers many points of 
interest to the geologist. Where the slates are in immediate contact with the granite 
they have become highly micaceous, and crystals of a mineral closely resembling 
Andalusite, as well as Andalusite itself, occur in great abundance, in some places so 
much so as to form a constituent of the rock. Crystals of garnet are also very common 
in these rocks. Throughout the entire boundary of the slates and granite, the former 
have a persistent dip to the east and south-east, and are singularly free from contor- 
tions, showing that where the granite acted on them its force was applied slowly, and 
while it was in a fluid or at least a pasty condition from heat; no violent disturbance, 
but a steady upheaving force, which acted uniformly on the hardened massof the slates, 
and metamorphosed without crushing them: examples on a smail scale, showing this, 
are to be seen on the shore under Obelisk Hill. 
The slates which belong to the Lower Silurian group are not cleaved but foliated ; 
large wedge-shaped masses of them, many hundred yards in length, are included in 
the granite; and the author explained, that when two such rocks were in junction 
along the flanks of mountain ranges, the detached portions of the slate might be com- 
pared to almonds on the surface of a pudding; not that they penetrated to any great 
depth into the granite mass, as was the idea entertained formerly by some geologists, 
although they may appear to be interstratified with it in bands. 
Along the shores of Killiney Bay, lumps of granite are found containing galena, a 
small vein of which is observed in the slates close to their contact with the granite east 
of Killiney Railway Station. West of Toronto Terrace, the granite in some places is 
full of plumose mica. In the true granite north of the rock called Black Castle, a 
large vein of euritic granite occurs, 40 yards thick, with many smaller veins formed 
chiefly of quartz and felspar. Many instances were given of euritic or Elvanite veins 
which cut through the granite and slates, being themselves traversed by newer eurites. 
The elvanite or euritic granite veins are often faulted, and the cracks thus formed 
filled up with infiltrated quartz. 
Thin parallel veins of elvanite are often bounded at either side by a thin layer of 
semi-transparent sub-crystalline quartz, possibly the result of segregation from the 
elvanite as it shrunk in the process of cooling. 
M. Du Noyer directed attention to a dyke-like tongue of granite in the hill north of 
Killiney Park, 3 feet 6 inches wide, which traversed the slates in a north and south 
direction. This dyke is cut across by elvanitic veins, which do not extend into the 
adjoining slates. He accounted for this singular fact by supposing that the main mass 
of the granite is close at hand below the surface, that the slates offered more resistance 
to forces disturbing both, and that the elvanite followed the lines of least resistance. 
The mica is very dark-coloured, and along the east wall of the dyke it is arranged in 
fine and well-defined laminz oblique to the wall. 
At aquarry north of the garden wall of Killiney Park, the junction of the slates and 
granite is well exposed. Here the dark mica assumes a remarkable appearance in 
the granite, being arranged in fine waved parallel lines which follow the direction of 
the boundary wall of the granite, and therefore dipping east at about 45°; hence the 
granite here has a stratified look. This singular foliation, as it may be called, of the 
mica crystals in the granite is best developed at the distance of a few feet from the 
slates, but it extends into the mass of the rock for the distance of about 20 feet, when 
it gradually dies out and the granite assumes its normal appearance; close to the 
slates the mica in the granite is disposed in small but well-defined blotches for the 
