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Published online by Cambridge University Press: 01 May 2009
There is, perhaps, no question of greater interest in the whole A range of physical geography than the circumstances that have determined the existence on the earth's surface of large and comparatively unbroken areas of land and water, involving as it does the debateable subject of marine and sub-aerial denudation, and the careful weighing of evidence on the just apportionment of these operations and of oscillations of level that have brought about the existing boundaries of sea and land.
Read at the Liverpool Meeting of the British Association, 1870.
page 545 note 2 It is true that both Gibraltar on its eastern face and Apes Hill on the African coast facing the north present cliff-like contours, bat in neither case are these on the present sea-board: most of the Gibraltar escarpment is separated by an intervening deposit of sand, and is not washed by the sea, and the face of Apes Hill is set back from the sea by an intervening undercliff; and I am inclined to attribute to both, escarpments an earlier origin than the existing coast-line of the Straits. The Gibraltar escarpment appears to be on a line of fault which is risible in the lime-stone at the southern extremity of the peninsula near Europa Point.
page 549 note 1 Sir O. Lyell stated in the discussion that the existence of a reverse current at a greater depth had been disproved.
page 552 note 1 Mr. James Smith, of Jordan Hill, in his description of the geology of the rock (Quart. Journ.Geol. Soc, vol. ii., page 41), records the occurrence of Patella ferruginea, a recent Mediterranean species, at a height of 700 feet, and notices the evidences of old sea margins at various heights extending nearly te its summit. I cannot, however, admit that these recent oscillations of level can, as Mr. Smith supposes, be eorrelated with the various dislocations the limestone formation has undergone. On the upper part of the western face there is a general sloping sub-aerial contour which has superseded all surface evidences of structural dislocations, and both the denudation producing this western slope, and the occasional evidences of higher shore-lines superimposed on it, must have been infinitely more recent than the great dislocations of the limestone strata.
page 553 note 1 It is sufficiently compact to be extensively quarried for building purposes. The city of Cadiz is almost exclusively built of it.