The substitution of land for a stretch of sea, in the Mediterranean, could not fail to cause the summer heat to be more intense in the region to the north than at the present time, while the increased elevation would produce a greater severity of winter cold, as Mr. Godwin Austen has pointed out in the case of the hills of Devonshire. When, indeed, we consider that the pleistocene land surface extended from the snowy heights of Atlas, as far north as the 100-fathom line off the coast of Ireland, we might expect to find African animals, such as the spotted hyæna and Felis caffer, ranging as far north as Yorkshire, for the only barrier to their migration would be that offered by the severity of a pleistocene winter.
Mediterranean Coast-line comparatively modern.
The submergence of the barriers, and the constitution of the Mediterranean as we find it now, have probably taken place but a short time ago, from the geological point of view, though we know that for the last 3,000 years the coast-line has been on the whole unchanged, except from the silting out of the sea by the sediment of rivers, such as the Po, and the elevation and depression of small areas by volcanic energy, as at Santorin. The physical character of the shores testifies to the truth of this view.
“On entering the Straits of Gibraltar,” Mr. Maw writes, “from the Atlantic, a notable change takes place in the aspect of the coast. Cape St. Vincent, on the Atlantic coast, presents a bold line of cliffs to the sea, and bluff cliffs extend many miles towards the Straits; but as soon as these are passed, a change of coast-form takes place, which must be noticeable to every observer. Cliffs on the sea-board become the exception, and the general line of the coast is merely a shelving under the sea of the general hill-and-valley system of the land, the sea running up all the depressions, and the land elevations spreading out into the sea with scarcely any abrupt cliff-line of demarcation. The uneven sea-bottom of the Straits seems to be a continuation of the contour of the adjacent land, consisting of rolling alternations of hill and valley, which must have received its conformation by subaerial agencies.”
“Corsica, and the adjacent islands of Elba, Capraja, and Monte Christo, are also remarkable for the absence of cliffs, and are wanting in those abrupt escarpements separating land and water which are so abundant on our own coasts. Their aspect is that of mountain-tops rising out of the sea, suggesting to the eye the seaward prolongation of their subaerial contour of sloping hillsides and river-cut valleys, as though the sea had not stood sufficiently long at its present level to excavate an escarpement. The deep intersecting bays that occur along the coast from Marseilles to the Riviera suggest the same conclusion, the undulating land surface spreading down to the water’s edge, and the deep bays running up the intervening valleys, which must have had an origin common with that of their landward prolongations.”
It is impossible to shut our eyes to the full force of this reasoning. The present aspect of the Mediterranean is, geologically speaking, a thing of yesterday.
Changes of Level in the Sahara coincident with those in the Mediterranean.
But if the Mediterranean area has been depressed to an amount of from 2,000 to 3,000 feet since the pleistocene age, we have proof that the region to the south has been elevated to that extent in comparatively modern times. Mr. Maw,[258] in his journey in 1873 to the Northern Sahara, observed raised beaches at a height of 2,000 feet, and loam and shingle-beds as high as 2,700 feet. He therefore concludes that the part of the Sahara which he explored had been raised at least 3,000 feet above the sea. These changes of level, the same in amount, but in opposite directions, were probably compensatory and simultaneous. Northern Africa may have been cut off from the central and southern portions of the continent by the sea extending over the Sahara, during the time that the Mediterranean was represented by the two inland salt lakes figured in the accompanying map ([Fig. 129]). And while the region of the Sahara was being elevated, that of the Mediterranean was probably being depressed.
These changes in the relation of sea to land, and the greater elevation of the mountains in the neighbouring countries, must have affected not merely the climate of southern, but also of north-western Europe, and ought not to be left out of account in any theory relating to pleistocene climate.