Little of the boulder clay can be seen today, except when digging the foundations of a new house or building. In the late 1880s, Dr Traill organised the digging of trenches in the area east of today’s airfield. He collected many exotic stones and send them south to Edinburgh for the attention of the renowned geologists, Peach and Horne.  Their list of the Traill’s stones is below.

Peach and Horne (1893) recognised that many of the rock types closely resemble rocks found around the basin of the Moray Firth. For example, the specimens of gabbro, epidiorite, and hornblende schist, are extremely like the rocks stretching from Portsoy south-westwards to the high grounds of Aberdeenshire. The marble may also have been derived from the same region, while the quartzites, quartz-schists, and mica-schists, very closely resemble the Dalradian strata of these types extending from Banffshire to Perthshire. The specimens of chalk and chalk flints are like blocks of the same materials met with in the drift of Banffshire and Aberdeenshire, dredged, along with fragmented seashells, from the bed of the Moray. In short, the great curving flow of the last great ice sheet – turning first N out of the Moray Firth, then NW and finally towards the W – passed over North Ronaldsay on its way to the shelf edge in the North Atlantic.

A walk around the shoreline today allows the keen observer to find many similar rocks. Please photograph them, if you wish, but leave them for others to observe. There should also be a very few Norwegian erratics – rhomb porphyry, larvikite as perhaps the most distinctive rocks – because those are found on Sanday and on Fair Isle. And the many gneisses stones may include some from Scandinavia. A definite find of a Norwegian erratic would be interesting!

Peach, B.N., Horne, J., 1893. On the occurrence of shelly boulder clay in North Ronaldsay, Orkney. Transactions of the Edinburgh Geological Society 6, 309-313.