On the surface geology of the Forth round Borrowstounness

Abstract

I. Preglacial Period. Buried River Channels. —Any respectable chart of the Firth of Forth shows a nearly semicircular bay extending for about three miles along the north shore opposite Borrowstounness, from the rocky promontory of Crombie on the east, to the quaint old royal burgh of Culross on the west. The ruinous pile of walls and chimneys—the remnants of the old coal and salt works of Preston Island—which rises picturesquely like some old fortress in the centre of the bay, is built on the north end of a low reef of rocks which stretches away into the Firth in a south-westerly direction, but at no point approaches within three quarters of a mile of the shore. A flat expanse of gray mud, dotted with patches of gravel and black boulders, sweeps round the bay at low tide, forming a deep ‶loop″ in the broad belt of alluvium which fringes the shores of the estuary. This bay, with its rocky islet, presents many features of interest to the student of denudation, and raises many a curious question. How, for example, does it happen that it is the only indentation of its kind on the north shore of the firth? and why it is that not a trace of rock is to be seen protruding through the flat zone of sleech which stretches round the bay between the rocky islet and the equally rugged shore? The fact that this island—unlike all the others in the firth—is composed not of greenstone but of bedded