The rock underlying the Laich of Moray is predominantly sandstone. However this deceptively simple statement covers a remarkable geological story.
The geological record contains two major successions of sandstone, the Old Red Sandstone (ORS) and the New Red Sandstone (NRS). Both successions were formed in desert or arid conditions, as what is now Scotland was moved by the forces of plate tectonics from somewhere near the South Pole northwards across the Equator to its present position in the northern Hemisphere.
The Old Red Sandstone was laid down in the Devonian period, between 415 and 360 million years ago, when Scotland lay south of the Equator, roughly at the latitude of the present Kalahari Desert. The period is named after the county of Devon, where ORS is very common.
The New Red Sandstone was laid down in the Permian and Triassic periods, when Scotland was roughly at the latitude of the present Sahara Desert, about 200 to 300 million years ago.
Between the Devonian and Permian Periods was the Carboniferous period, when Scotland lay close to the Equator, and lush tropical vegetation eventually decomposed to form the coal which is found in Central Scotland. The Carboniferous, however is entirely missing from the Laich of Moray; 250-million-year-old Permian rocks lie directly on top of 350-million-year-old Devonian rocks. So the coal, if any was ever actually formed in the Laich of Moray, must have been eroded away before the NRS was deposited, leaving a gap of 100 million years in the geological record of the Laich. This sort of gap in the succession is called an unconformity.
When geologists first started studying the geology here, the rocks all look similar, all being desert sandstones. Fossil fish were fond in several localities which could be used to show that the rocks where they were found were of Devonian age. Because all the sandstone was similar, it was at first assumed that it was all ORS.
Then more fossils, the Elgin reptiles, were discovered in the Cuttieshillock and the nearby Hopeman sandstone. The reptiles have been given names which reflect their place of origin, including Geikia elginensis ('Geikia' after the eminent 19th century geologist Sir Archibald Geikie), Elginia and Gordonia (after the Rev George Gordon, minister at Birnie and a very respected naturalist, who collected many of the specimens). Elgin Museum has an excellent display of the Elgin reptiles and other local fossils.
These discoveries were of major significance, because until then no land-living animals had been found in the Devonian, and the Elgin reptiles resembled species known to be of much younger age.
Thus the discovery of land-living reptiles forced a reappraisal of the age of the rocks, and in due course the answer was found in the form of the unconformity, where the NRS lies at a slight angle on top of the ORS, with just a thin bed of pebbles marking the gap of 100 million years.
As well as the actual reptile body fossils, many trace fossils have been found in the form of trackways. These footprints of reptiles walking across the sand dunes, preserved in the lithified sand. There is a display of such trackways at the entrance to Clashach Quarry, and many more have found their way into Elgin and other museums.
Just for the avoidance of doubt, the Elgin reptiles are not dinosaurs. They are in fact much older than the dinosaurs, which flourished between 65 and 145 million years ago, in the Cretaceous period.
Until recently, geologists were not even certain whether the ORS of the Laich of Moray belonged to the late Permian or the early Triassic. Then, in the late 1990s, quarrymen at Clashach Quarry near Hopeman found a block with a rusty-looking cavity in it. They took it to a local geologist who had been working with them on the reptile trackways and had interested them in the geological implications of the trackways. She realised the potential of the cavity, and took it to the experts. Thanks to the use of an MRI scanner, it was possible to create an image of the cavity without destroying it, and it turned out to be the skull of a known species of reptile called a dicynodont, and finally enabled the Hopeman sandstone to be dated as late Permian.
The groundbreaking block of sandstone is on display in Elgin Museum, along with a model of the skull. You can read all about it at Link