and Magee, and Scrabo Hill in Co. Down. The area of the
basaltic plateau may be roughly estimated at 2,000 square miles.

[Illustration: Fig. 27.--"The White Rocks," Portrush, Co. Antrim,
showing the plateau-basalt resting on an eroded surface of the Upper
Chalk, with bands of flint.--(From a photograph.)]

The truncated edges of this marginal escarpment rising to levels of
1,000 to 1,260 feet, as in the case of Benevenagh in Co. Derry, and
1,825 feet at Mullaghmore, attest an originally greatly more extended
range of the basaltic sheets; and it is not improbable that at the close
of the Miocene epoch they extended right across the present estuary of
Lough Foyle to the flanks of the mountains of Inishowen in Donegal in
one direction, and to those of Slieve Croob in the other. In the
direction of Scotland the promontories of Kintyre and Islay doubtless
formed a part of the original margin. Throughout this vast area the
volcanic lavas rest on an exceedingly varied rocky floor, both as
regards composition and geological age. (See Fig. 28.) Throughout the
central, southern, eastern, and northern parts of their extent, the
Chalk formation may be considered to form this floor; but in the
direction of Armagh and Tyrone, towards the southwestern margin, the
basaltic sheets are found resting indiscriminately on Silurian,
Carboniferous, and Triassic strata. The general relations of the
plateau-basalts to the underlying formations show, that at the close of
the Cretaceous period there had been considerable terrestrial
disturbances and great subaerial denudation, resulting in some cases in
the complete destruction of the whole of the Cretaceous strata, before
the lava floods were poured out; owing to which, these latter are found
resting on formations of older date than the Cretaceous.[3]

[Illustration: Fig. 28.--Section across the volcanic plateau of Antrim,
from the Highlands of Inishowen, Co. Donegal, on the N.W., to Belfast
Lough on the S.E., to show the relations of the volcanic rocks to the
older formations.--B. Basaltic sheets breaking off in high escarpments;
T. Trachyte porphyry of Tardree mountain rising from below the newer
plateau-basalts; C. Upper Chalk with flints; N.R. New Red marl and
sandstone (Trias); M. Metamorphic beds of quartzite, various schists and
crystalline limestone; F. Large fault.]

[1] Mr. J. Starkie Gardner, from a recent comparison of the
plant-remains of Antrim and Mull, concludes that "that th