Erratics

Erratics have been mentioned in The Diary before, but it seems that, the more we walk these hills, the more of them we find. The ones that stand out are those that are perched on the top of hills, like this one immediately to the north of Ockle. If they're further down a slope, it's difficult to decide whether they are erratics - stones which have been moved by the glaciers during the Ice Age some 10,000 or more years ago - or random rocks that have fallen down the hill.

Sometimes it's easy to tell because the rock is formed of a rock which simply doesn't 'belong' here. This one, high above Orsmaigmore, is a granite. The nearest granite is at Strontian, and the composition of this one doesn't look like the pale-coloured Strontian granite.

The biggest often sit on bare rock. This one is on Sidhean Mor, a low hill immediately to the south of Achnaha. It's part of a family of three big rocks, strung out along a ridge.

Erratics can be useful to geologists. If the rock can be traced to particular place - for example, there is one near Ormsaigbeg which is clearly formed of Strontian granite - then the course of the glaciers can be worked out.