View source for Basement Complex of Orkney

=== The pre-Old Red Sandstone land surface ===
Prior to the deposition of the Old Red Sandstone the basement inliers appear to have formed arrange of hills which was elongated in a north-north-westerly direction. The present topography of the inliers appears to be much the same as it was at the time of their burial, and small patches of sediment can still be found on the hill tops of Yesnaby and Graemsay. The original hills may not have been more than 100&nbsp;m high and the original average gradients of their slopes did not normally exceed 13°, but there is ample evidence for the presence of small cliffs, knolls and gullies. The granite and metamorphic rock underlying the exhumed surface is everywhere fresh and there is no sign of any deeply weathered proﬁle.