nded margin,
above the floor of Chalk which formed the surface of the ground.[2]
(Fig. 27.) At Templepatrick the columnar trachyte may be observed
resting on the Chalk, or upon a layer of flint gravel interposed between
the two rocks, and which has been thrust out of position by a later
intrusion of basalt coming in from the side.[3] It is to be observed,
however, that the trachytic lavas nowhere appear cropping out along with
the sheets of basalt around the escarpments overlooking the sea, or
inland; showing that they did not spread very far from their vents of
eruption; a fact illustrating the lower viscosity, or fluidity, of the
acid lavas as compared with those of the basic type.

(_d._) _Second Stage._--After an interval, probably of long duration, a
second eruption of volcanic matter took place over the entire area; but
now the acid lavas of the first stage are replaced by basic lavas. Now,
for the first time, vast masses of basalt and dolerite are extruded both
from vents of eruption and fissures; and, owing to their extreme
viscosity, spread themselves far and wide until they reach the margin of
some uprising ground of old Palaeozoic or Metamorphic rocks by which the
volcanic plain is almost surrounded. The great lava sheets thus produced
are generally more or less amorphous, vesicular and amygdaloidal, often
exhibiting the globular concentric structure, and weathering rapidly to
a kind of ferruginous sand or clay under the influence of the
atmosphere. Successive extrusions of these lavas produce successive
beds, which are piled one over the other in some places to a depth of
600 feet; and at the close of the stage, when the volcanic forces had
for the time exhausted themselves, the whole of the North-east of
Ireland must have presented an aspect not unlike that of one of those
great tracts of similar lava in the region of Idaho and the Snake River
in Western America, described in a previous chapter.

(_e._) _Third Stage (Inter-volcanic)._--The third stage may be described
as inter-volcanic. Owing to the formation of a basin, probably not deep,
and with gently sloping sides, a large lake was formed over the centre
of the area above described. Its floor was basalt, and the streams from
the surrounding uplands carried down leaves and stems of trees, strewing
them over its bed. Occasionally eruptions of ash took place from small
vents, forming the ash-beds with plants found at Ballypallidy, Glenarm,
and along the