s--in other words, the pipes filled with either solid basalt, or
basalt and ashes--are still to be found at intervals over the whole
area. Owing to the greater solidity of the lava which filled up these
"necks" over the plateau-basaltic sheets which surround them, they
appear as bosses or hills rising above the general level of the ground.
One of these bosses of highly columnar basalt occurs between Portrush
and Bushmills, not far from Dunluce Castle, another at Scawt Hill, near
Glenarm, and a third at Carmoney Hill above Belfast Lough. But by far
the most prominent of these old solidified vents of eruption is that of
Sleamish, a conspicuous mountain which rises above the general level of
the plateau near Ballymena, and attains an elevation of 1,437 feet above
the sea. Seen from the west, the mountain has the appearance of a
round-topped cone; but on examination it is found to be in reality a
huge dyke, breaking off abruptly towards the north-west, in which
direction it reaches its greatest height, then sloping downwards towards
the east. This form suggests that Sleamish is in reality one of the
fissure-vents of eruption rather than the neck of an old volcano. The
rock of which it is formed consists of exceedingly massive,
coarsely-crystalline dolerite, rich in olivine, and divided into large
quadrangular blocks by parallel joint planes. Its junction with the
plateau-basalt from which it rises can nowhere be seen; but at the
nearest point where the two rocks are traceable the plateau-basalt
appears to be somewhat indurated; breaking with a splintery fracture and
a sharp ring under the hammer, suggesting that the lava of Sleamish had
been extruded through the horizontal sheets, and had considerably
indurated the portions in contact with, or in proximity to, it.[6]
Amongst the vents filled with ash and agglomerate, the most remarkable
is that of Carrick-a-raide, near Ballycastle. It forms this rocky island
and a portion of the adjoining coast, where the beds of ash are finely
displayed; consisting of fragments and bombs of basalt, with pieces of
chalk, flint, and peperino, which is irregularly bedded. These ash-beds
attain a thickness of about 120 feet just below the road to Ballycastle,
but rapidly tail out in both directions from the locality of the vent.
Just below the ash-beds, the white chalk with flints may be seen
extending down into the sea-bed. Nowhere in Antrim is there such a
display of volcanic ash and agglomera