Geoscientist Online

As geologist and science writer Nina Morgan* discovers, a little geochemistry goes a long way

Archibald Geikie (1835 – 1924), cut his geological teeth with studies in Edinburgh and the Hebrides, and in the 1860s worked with Roderick Murchison (1792 – 1871) to untangle the complex geology of the northwest highlands. Although the Murchison – Geikie interpretation was debunked by the work of other geologists in the 1880s, Geikie went on to become director of the Scottish Geological Survey in 1882.

Geikie had many other strings to his bow. He was a gifted writer and author of a number of textbooks and popular books about geology. In addition, he was keen observer of geology in the urban environment. In his book, A Long Life's Work: An Autobiography, he recalled:

"In the course of my journeys all over Scotland there was always an interest in examining the tombstones in graveyards, first for the light which they so often throw upon the families that have lived for generations in a district... and next for the valuable and unexpected information which they frequently afford as to the manner and rate of decay which various kinds of stone, employed for monumental purposes, suffer from the disintegration effects of the atmosphere."

Losing your marbles

His observations on weathering in gravestones soon led him to conclude that acid rain – essentially carbonic acid (H2CO3) formed when carbon dioxide (CO2) emitted from the burning of coal was dissolved in rain water – was a major culprit. The effects, he noted, were especially obvious on marble, a stone often chosen for high-status graves. As an illustration, he cites the degradation of the gravestone in Greyfriars churchyard in Edinburgh honouring the chemist Joseph Black (1728 – 1799).

"This sumptuous tombstone," Geikie noted, "consisted of a solid framework of hard siliceous sandstone into which a large upright slab of white marble had been firmly fastened, recording in Latin, with pious reverence, the genius and achievements of the discoverer of Carbonic Acid, and Latent Heat, and adding that his friends wished to mark his resting place by the marble while it should last."

No doubt those well-meaning, but perhaps chemically illiterate friends imagined the marble would last a lot longer than it did. When Geikie visited Black's grave in 1879, less than 80 years after it had been erected, he noted that the inscription on the marble was becoming illegible and worse:

"...The slab, still firmly held in place by the metal fastenings all round its margin, had bulged out considerably in the centre, forming a large blister-like expansion, which had been rent by numerous cracks."

By 1894 the marble had crumbled so badly that the Town Council of Edinburgh was forced to replace it with a slab of what Geikie described as a “far more durable sandstone, on which the original epitaph had been carefully copied."

Fit for purpose

The Council clearly recognised that Black's gravestone was worthy of preservation. But it would be difficult to justify spending considerable sums on renovating marble monuments to 'ordinary' citizens. Banning of the use of marble – seen as a prestigious material – for churchyard gravestones would certainly have proved unpopular. So when it came to honouring the dead, what was a town council to do?

Geikie had an answer. "A cynic may say that, in the vast majority of cases, it will be no great matter if, at the end of a hundred years, a marble monument has become illegible, or fallen to pieces, and that people may be allowed to put up memorials in this perishable material which in most cases is likely to last at least as long as the memory of the deceased." So much for immortality!

Acknowledgements

Sources for this vignette include: A Long Life's Work: An Autobiography by Sir Archibald Geikie, Macmillian, 1924; the Wikipedia entry for Joseph Black; and the Dictionary of National Biography entry for Sir Archibald Geikie by David Oldroyd. I also thank the Haslemere Educational Museum for making available Geikie's field notes about Greyfriars Churchyard.

Nina Morgan is a geologist and science writer based near Oxford.  Her latest book, The Geology of Oxford Gravestones, is available via www.gravestonegeology.uk