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1851.] FORBES ON THE OOLITES IN SKYE. 105 



on a cruise in his yacht to Mull and Skye, and so examine at our 

 leisure the desired places. Accompanied by Professor Goodsir of 

 Edinburgh, accordingly we set sail, and in the course of three weeks' 

 cruise had not only the good fortune to see the geological points in 

 question, but also to add not a few fossils and nearly twenty species 

 of living animals to the British fauna. 



The peninsula of Trotternish, which forms the north-western por- 

 tion of the island of Skye, presents on its northern line of sea-coast 

 a range of magnificent cliffs, extending from Portree to Loch Staffin. 

 The crest of these cliffs is composed of a vast bed of imperfectly 

 columnar trap, resting on oolitic sandstones, limestones, and shales, 

 the uppermost of which were determined by Sir Roderick Murchison 

 to be the equivalents of the cornbrash and forest marble. Beneath these 

 we find unquestionable representatives of the middle and inferior 

 oolitic strata, and at the base of all undoubted lias. They abound 

 in fossils, and, whenever the palaeontology of the secondary rocks of 

 Scotland shall be scientifically explored, will afford a rich harvest 

 of beautiful and probably undescribed forms of invertebrata to the 

 naturalist who may have the good fortune to undertake the work. 



Through the oolitic strata are seen rising dykes of greenstone in 

 communication with the spread of trap above, and other trap dykes 

 are seen which not only burst through the greenstone, but also 

 through the sheet of trap forming the perpendicular wall on the 

 summit of the cliffs. 



Diagram of the Geological Structure of Trotternish in Skye. 



a. Lias. e. Estuary shales. 



b. Inferior oolite. /. Oxford clay. 



c. Middle oolite. g. Amygdaloidal trap. 



d. Imperfectly columnar basalt. 



The strata of the cliffs dip rapidly inland southwards at a consi- 

 derable angle, and a little way behind them towards the east. Far- 

 ther back towards the west rise lofty hills of amygdaloidal and zeo- 

 litic trap, which, broken up into fragments on these escarpments, 

 form magnificent isolated blocks and pinnacles of rock of vast height 

 and slenderness, resembling so many gigantic castles and towering 

 spires of dimensions beyond the workmanship of human architecture. 

 The truly wonderful scenery of the Storr and Quiraing, which far 

 surpasses for irregularity any other rock landscapes in Britain, have 

 been produced by the breaking up of this amygdaloidal escarpment. 



The cause of this extraordinary range, extending over many miles, 

 of cyclopean ruins, depends upon the fact which it is my object to 

 announce in this communication. Between the mass of amygdaloidal 

 trap and the columnar trap which crests the sea-cliffs and dips in- 



VOL. VII. PART I. I 



