Great Geologists | 81
Simplified geological cross-section across the North-West Highlands
showing the main rock units present and their relationship as
understood today.
John Horne was born on 1 January 1848, in Campsie,
Stirlingshire. He was educated at Glasow High School and
the University of Glasgow. He joined the Scottish Branch of
the geological survey in 1867 as an assistant and became an
apprentice to Ben Peach. The two soon became good friends
and collaborators. Horne was a logical thinker and writer,
complementing Peach’s skills of creative thinking to resolve
complex geological structures.
Geological map of the North-West Highlands region mapped by Peach
and Horne. Adapted from Butler (2010).
When posted to northern Scotland, working for the coastguard,
he collected fossils from the Durness Limestone that aroused
Murchison’s interest in the geology of the region and, in effect,
initiated the Highlands geological controversy. There is some
irony that it was Ben Peach who contributed to its resolution
— on Murchison’s recommendation, Ben had been educated
at the Royal School of Mines in London, and then joined
the Geological Survey in 1862 as a geologist, moving to the
Scottish branch in 1867.
Peach and Horne worked on many various aspects of Scottish
geology, including mapping in the Southern Uplands and in the
coal belt of the Central Lowlands. Here, Peach took a special
interest in the Carboniferous crustacean fossils he collected,
later describing them in a major monograph. They also took
geological holidays together that resulted in publications — on
Orkney and Shetland, for example. But it was in the North-
West Highlands that they made their greatest mark, unravelling
the complex geological structures and producing a definitive
map of the region.
Although the idea of horizontal movement along low-angle
detachment surfaces had been discussed by Alpine geologists
as early as 1841, in Britain, faults were largely considered as
vertical features. It did not take Peach and Horne and their
team long to realise that thrusting was the dominant structural
style in the North-West Highlands (indeed, so rapidly was
Geikie converted to this view, that it was he who introduced
the term ‘thrust plane’). By 1884, they had published their first
paper to explain this, although a full description in the memoir
accompanying the geological map took an additional 20 years