soft pastel on board,
43cm x 43cm,
Iain White, 2016,
This stylised soft pastel shows Ben Stack across Lock Stack and to that extent is similar in subject to No.16, though different in treatment. Unlike Arcuil and Foinne Bheinn, Ben Stack is a mountain almost entirely composed of Lewisian Gneiss.
The Ben Stack line (originally proposed by Ben Peach) marks the boundary between the northern (Laxfordian ) area of the Lewisian and the central (Scourian) section. Ben Stack itself is largely comprised of Scourian orthogneiss with a number of basic dykes running through it, the north extent of the Scourie Dyke Swarm.
That Ben Stack remained as an isolated hill seems to be because the ice stream flowing northwest from what is now Loch More split at Achfary, part flowing to the west along Stath Stack, part flowing along the line of Loch Stack towards the coast at Loch Laxford.
Clearer here is that along the lower slopes of Ben Stack adjacent to the western shore of Loch Stack is an atlantic outlier of the Boreal Deciduous Forest (green pastel) that runs through Scandinavia and northern Eurasia south of the Arctic Tundra. In Scotland these primary boreal woodlands were principally dominated by birch particularly the hairy birch, Betula pubecens.
Now rare themselves, where these outliers survive they are important for their equally rare atlantic bryophyte and pteridophyte flora that festoons the tree bark and the surface of rocks on the woodland floor. Notable amongst these are the filmy ferns such as Hymenophyllum wisonii.