File:GSG GLA FROCOV.jpg

Cover picture: View looking NNW up Loch Lomond from the hill of Duncryne [NS 435 859], near Gartocharn. To the left are the hills around Luss where slate was once extensively quarried. The distant jagged hill left of centre is Ben Arthur ("The Cobbler"): Ben Lomond is the snow-covered mountain right of centre. All these hills are part of the Dalradian block, eroded by ice and water from schistose greywackes, mica schists and slates.

On the right the village of Balmaha can be seen along the shore of the loch: the wooded ridge behind is the westerly continuation of Conic Hill, formed of steeply-dipping conglomerates of the Lower Old Red Sandstone. These rocks continue to the left as wooded islands across the loch. Between these ridges and the higher ground of Dalradian rocks to the north, lie the Highland Border Complex and the Highland Boundary Fault. This fault is a terrane boundary separating the Dalradian block from the Midland Valley block: in Ordovician times these two terranes had such entirely different histories that they could not then have been adjacent to one another.

The foreground is underlain by soft, easily eroded sandstones and mudstones of the Lower Old Red Sandstone. The hill of Duncryne, composed of agglomerate and basalt, is an eroded volcanic plug of Lower Carboniferous age.