Access to the far north of Scotland has never been easy. This very early geological map by Philippe Buache dated 1746 suggests that the only rock known to be there at that time was marble.
By the start of the 19th century, geologists were beginning to examine regions in some detail. In 1819, Dr John MacCulloch published a work in three volumes, A Description of the Western Isles of Scotland… which remained the classic account of the geology of the area for at least fifty years. His research took him to the north-west coast of the mainland, and his analysis shows that he had a good understanding of exactly what rocks were found there.
The coast itself is dominated by gneiss, a metamorphic rock that is the oldest in the British Isles. The mountains that rise up so spectacularly are composed of red sandstone, which lies unconformably over the gneiss. Over this sandstone, there might also be found some distinctive white quartzite. When MacCulloch examined this quartzite, he noticed that some of it contained ‘imbedded cylindrical bodies’. This is now known as pipe rock, the ‘bodies’ thought to be worm burrows.
MacCulloch also noticed limestone regions, especially in the vicinity of Loch Eriboll, but he did not record all the different bands of rock that are found in the north-west region. What he did reveal was the confusion that was to puzzle geologists for some sixty years, and lead to a significant scientific controversy. Whilst the sedimentary sandstone and quartzite on the west coast lay, as expected, on top of the ancient gneiss, further inland the succession was far from clear.
He observed gneiss lying not just underneath, but also above the sandstone, quartzite, and limestone. How was it possible for gneiss, the oldest rock in the British Isles, and one that had spent thousands of years below the earth’s crust undergoing a process of metamorphosis, to be seen lying on top of rocks that were simply lying unaltered where they had been laid down on the earth’s surface? Worse still, the sedimentary layers showed no regular structure: sometimes limestone was above the quartzite, sometimes below it, and sometimes there were two layers of quartzite with the limestone wedged between them.
Another visitor to the area, Robert Hay Cunningham, published a superb geological survey in 1841, his Geognostical Account of the County of Sutherland. He found more sedimentary layers – what are now called the fucoid beds, for example – and confirmed the picture of confusion that MacCulloch had painted, as this section from his essay shows. Cunningham also supplied the first geological map of the county, which completed a hugely impressive survey. Had he lived longer, one cannot help but suspect that the controversy would have been resolved a good deal sooner, but sadly, he died at the age of 27.
The north-west of Scotland had also been visited by the man who was to dominate much of the geological thinking in Britain during the 19th century. Sir Roderick Impey Murchison was a figure every bit as impressive as his name suggests. He was in his thirties when he took up science; previously he had been in the army and seen action during the Napoleonic wars. Finding civilian life a little dull, he immersed himself in the study of geology, and within a few years, had published one of the most important works of that time, titled simply Siluria. His examination of the rocks of the Welsh and English borderlands had led to a whole new geological system of that name, and he was known as the King of Siluria. Such was his standing that he was knighted in 1846, and in 1855 appointed Director General of the British Geological Survey, which was gradually surveying the entire country in great detail.
On his trip north in 1827, Murchison was accompanied by the notable geologist Adam Sedgwick, Professor of Geology at Cambridge. Their main aim had been to study the red sandstone of the east coast, but they did head west and ventured down Loch Eriboll, where they observed the strata, including the double layer of quartzite that Cunningham had noted in his section.
Murchison felt very drawn to this part of Scotland. His ancestors had at one time been castellans of Eilean Donan Castle, and one of them, Donald Murchison, had been bold enough to challenge the authority of the English government after the 1715 Jacobite rebellion had been suppressed. Sir Roderick erected a memorial to Donald, which can still be seen on the shores of Loch Duich.