The Ancient Volcanoes of Great Britain, Volume 2 (of 2)Geikie, Archibald
Science
The Ancient Volcanoes of Great Britain, Volume 2 (of 2)
Geikie, Archibald
Volcanoes -- Great Britain
Some idea of the importance and interest of the volcanic area of
Eastern Fife may be gathered from the fact that in a space of about
70 square miles no fewer than 60 necks may be counted, and others are
probably concealed below the drift-deposits which cover so much of the
interior of the country. The area of this remarkable display extends
from St. Andrews Bay and the Vale of the Eden southwards to the coast
of the Firth of Forth between Lundin Links and St. Monans. All over the
inland tract the necks form more or less marked eminences, of which the
largest are conspicuous landmarks from the southern side of the Firth.
But the distinguishing characteristic of the area is the display of the
necks along the coast, where, in a series of natural dissections, their
form, composition, internal structure and relations to the surrounding
rocks have been laid open in such clearness and variety as have been
met with in the volcanic records of no other geological period within
the compass of these islands. As this district thus possesses a
singular interest and value for the study of volcanic vents, I shall
enter in some detail into the description of the sections so admirably
laid bare.
[Illustration: Fig. 210.--View of small neck in Calciferous Sandstones,
on the shore, three miles east from St. Andrews.
(This illustration, likewise Figs. 212, 216, 219, 221, 222, 225 and 227
are from photographs taken for the Geological Survey by Mr. R. Lunn.)]
As in Ayrshire, the necks in the East of Fife generally rise as
isolated conical or dome-shaped hills, with smooth grassy slopes, but
where a dyke or boss of basalt occurs in them, it usually stands out
as a crag or knoll. Largo Law (Fig. 209) may be taken as a singularly
perfect example of the cone-shaped neck. This hill, however, comprises
more than one vent. The mass of tuff of which it consists probably
includes at least three distinct funnels of discharge, and surrounding
it there still remains a good deal of the fragmental material that
gathered around these vents and is now seen to lie unconformably upon
the Carboniferous formations (Fig. 208). There must be a total area
of not much less than four square miles over which tuff occupies the
surface of the ground.
While the Fife necks possess the great advantage of having been laid
bare by the sea, their frequent small size on the coast allows their
whole area to be examined. As illustrations of these little vents, two
plates are here given from the coast-line to the east of St. Andrews,
where a number of small necks of agglomerate have been planted among
the plicated Calciferous Sandstones. In Fig. 210 the abrupt truncation
of the sandstones by the volcanic rock is well shown. The strata on the
right have been broken through, and the sea has indented a small gully
along the wall of the old volcanic funnel. The sandstones in front,
however, still adhere firmly to the agglomerate, which rises above them
as a rugged mass of rock.
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