There is likewise a plane-tree,
the leaves of which seem to agree with those of Platanus aceroides (Figure 141
Chapter 14), and a fern which is as yet peculiar to Mull, Filicites hebridica,
Forbes.
These interesting discoveries in Mull led geologists to suspect that the basalt
of Antrim, in Ireland, and of the celebrated Giant's Causeway, might be of the
same age. The volcanic rocks that overlie the chalk, and some of the strata
associated with and interstratified between masses of basalt, contain leaves of
dicotyledonous plants, somewhat imperfect, but resembling the beech, oak, and
plane, and also some coniferae of the genera pine and Sequoia. The general
dearth of strata in the British Isles, intermediate in age between the formation
of the Eocene and Pliocene periods, may arise, says Professor Forbes, from the
extent of dry land which prevailed in that vast interval of time. If land
predominated, the only monuments we are likely ever to find of Miocene date are
those of lacustrine and volcanic origin, such as the Bovey Coal in Devonshire,
the Ardtun beds in Mull, or the lignites and associated basalts in Antrim.
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