Heatherbloom Pit

Some 40 million years ago, a river ran across this countryside, flowing past where you are presently standing on its way towards destination somewhere to the east. At that time the landscape of what is now the Buchan area would have looked totally different to now. Plants and animals would have been very different from those you are familiar with. Although the great dinosaurs had become extinct, the mammals which replaced them were only distant ancestors of present species.

Even more striking would have been the change in the shape of the land compared with the present day. You probably approached the site by walking over gently rising ground until you came to this quarry, but had you been standing here all those millions of years ago, you would have been on the floor of a valley, most likely surrounded by rolling hills, as illustrated in the first panel of this display board! The river would have been flowing swiftly over a bed of shiny white pebbles, exactly like the ones which you can see in the excavation in front of you. If you look closely, you will see that the pebbles are quite rounded – a sign of having been worn by flowing water. There are also layers of sand between the pebbles, marking periods when the flow of the river was slower. Many of these beds slope gently eastwards, suggesting that the ancient river flowed in that direction. The white pebbles are made of a very hard rock called quartzite. This is very similar to rock found around Durn Hill, just south of Portsoy on the Moray Firth coast. The ancient river flowed south-eastwards from the Durn Hill area to Windyhills, and then on towards what is now the North Sea, carrying these distinctive pebbles with it and dropping large number of them on its river-bed to form the materials you can see in the quarry.

What has happened to the hills, and why are river-bed gravels now positioned on high ground? The answer to this is illustrated in the second panel of the display board. From about 40 million years ago until about 10 million years ago, the climate of Scotland was warm and humid, almost tropical. Under such conditions many types of rock ‘rot’ – they disintegrate to form a sandy or clayey gravel. These rotted rocks are easily washed away by rain and river action, so the hills gradually were removed over the millennia. However, the layers of very hard quartzite pebbles laid down by the river on the former valley floor did not rot, but protected the ground beneath them, so that the rocks there did not get worn away. As the former valley sides lowered, so the valley floor stayed where it had been, until what had been low ground was left as the highest ground in the area, the position it is in at present (see panel 3 of the board). Therefore you are standing in a topsy-turvey landscape, where high ground has become low, and low ground high, all in the space of about 40 million years.