Geoscience Reference
In-Depth Information
The Scots' conclusions were confirmed by Jean-Fran¸ois Berger and
William Conybeare in 1816, and the scale swung in favour of the
Vulcanists, whose view was that basalt was derived from a molten
source. Additional evidence came from later observations made in
Italy and elsewhere of active and extinct volcanoes where the presence
of columnar basalt was seen in unequivocal lava flows, proving
beyond doubt that basalt was an igneous rock. Later still the mechan-
isms of fissure eruptions, which were unknown in the 1790s, were
fully comprehended and the origin of the Giant's Causewaymore fully
understood.
Late in life Richardson turned his pen to agricultural subjects
and wrote extensively on the merits of growing fiorin grass. He died in
September 1822, continuing to hold to his views on the nature and
origin of his 'sedimentary basalt'.
HUTTON RETURNS TO HIS THEORY
Given the initial criticism that his paper of 1785 had provoked,
Hutton decided to examine the geology of a number of sites in
Scotland. Setting off with John Clerk of Eldin, the engraver and water-
colourist, he visited the estate of JohnMurray, the 4th Duke of Atholl,
approximately 75miles north of Edinburgh, where he wanted to locate
the junction between the granite and the mica schist. In the bed of the
Tilt, a small river that flows through the steep-sided glen, Hutton
found what he was looking for: veins of reddish-coloured granite
cross-cutting the mica schist (Figure
6.4
). This was conclusive evi-
dence that the granite had been injected in a fluid state from below; it
was plutonic.
We should be grateful that Hutton was a friend of JohnMurray's.
Some 62 years later John Hutton Balfour, a cousin of Hutton's who
was Professor of Botany in Edinburgh, was in the company of some
botany students (who affectionately called him 'Woody Fibre'), and
together they tried to visit Glen Tilt in order to examine its plant life.
There, on 21 August 1847, they came up against George Murray,
6th Duke of Atholl, and his ghillies, who tried to deny them entry
