File:The Quarterly journal of the Geological Society of London (13369100573).jpg

404
PKOCEEDINGS 0E THE GEOLOGICAL SOCIETY. .April 30,
lying boulder-beds ; in otber places tbe latter rests on an eroded
surface of the former, and both are overlain by Boulder-clay of the
Drift-period (see figs. 1 & 2). The blocks of grit, derived either
from the Silurian or Old-Red-Sandstone formations, lying to the
northward, are sometimes from 18 inches to 2 feet in diameter, and
are not unlike those found in the Boulder-clay of the Glacial period,
though we failed to discover any very clear marks of ice-action on
their surfaces. It is difficult, however, to conceive how blocks of
such size, and so irregular in shape, could have been transported for
a distance of 20 or 30 miles (the nearest distance of their original
positions), except by the agency of floating ice ; and the absence of
ice-grooves and scratches on boulders of sandstone which have
undergone a certain degree of decomposition from their proximity to
the surface, cannot be regarded as a serious objection to the view
that the boulders themselves have been carried on ice-rafts.
Position of the Boulder-beds. — On referring to Griffith's Geological
Map of Ireland, it will be seen that the city of Armagh stands in
proximity to beds but little removed from the base of the Carboni-
ferous Limestone. There are, however, representatives of the New
Red Sandstone, which were observed by Mr. Egan in wells and
excavations beneath the centre of the city itself. As the Permian
beds dip in that direction, they no doubt pass below the New Bed
Sandstone ; so that their geological position is beyond question as
regards this formation (see fig. 3).
Fig. 3. Horizontal Section through the City of Armagh (1 m ile).
a. Drift.
c. Permian Boulder-beds.
h. New Eed Sandstone, resting on c.
d. Carboniferous Limestone.
e. Lower Silurian Eocks.
Their relations to the Carboniferous Limestone can also be clearly
determined at the quarries where the boulder-beds themselves are
seen. They lie upon beds within 300 or 400 feet of the base of the
Carboniferous Limestone, which is worked in numerous quarries in
the vicinity. These quarries are celebrated for the number and
variety of the fish-remains they have afforded, including some of the
type specimens of Agassiz's ' Poissons Eossiles,' now in Lord Ennis-
kiUen's collection.
Denudation of the Carboniferous Beds. — As in the north of England,
so in the north of Ireland, the amount of denudation which the
Carboniferous rocks have undergone before the deposition of the
Permian rocks, has been very great. In the case of Armagh, the
whole of the middle or " Calp " series, the Upper Limestone, the
Yoredale shales, Millstone-grit, and Coal-measures (which are largely