Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/414

Rh Glacial period had a greater extension northwards than it now presents. In the notes to the first part of his 'Cosmos,' Humboldt quotes a passage in which that wonderful old geographer. Strabo—the accuracy and minuteness of whose observation I have often had occasion to admire when accompanying my friends, Captain Graves and his officers, during their surveying labours on the coast of Asia Minor—distinguishes two kinds of islands, those which have been detached from the mainland, and those which have arisen from the sea. Now, though the islands situated in the region of the Atlantic, between the Gulf-weed bank and the Old World, are in great part of volcanic origin, in each group there are fossillferous strata of sedimentary origin and meiocene age, all so related to the corresponding beds in Europe that they must be undoubtedly regarded as the fragments of the upheaved bed of an uniform shallow meiocene sea.

In the Madeira group the tertiary limestone, according to Mr. Smith, forms the base rock of the Isle of San Vincente, and in Madeira itself is elevated to a height of 2,500 feet, "a change," writes the observer, "previous to the ejection of the overlying volcanic products." Mr. Smith states also that there are no evidences, in that island, "of elevation fof [sic] the land during or subsequent to the volcanic period—though strong indications of subsidence."—(Geol. Proceedings, vol. iii. p. 351.) The meiocene limestone of St. Mary's, in the Azores, which includes Pecten latissimus, and other well-marked fossils, will also probably be found, on examination by a competent observer, to be more ancient than the volcanic rocks of that region. In the Canaries and Cape de Verde Islands there are also tertiary marine strata, apparently of meiocene age, and fragments of the same great sea bed with those in the other East Atlantic Islands. That these islands are all, when geologically considered, parts of one system of land, anciently continuous, and belong to Strabo's first class, agrees with their botanical and zoological character as part of one (the great Mediterranean) province. Their floras are all closely related to those of the nearest mainland, and are also mutually related through endemic plants to each other.

Out of 596 species of flowering plants, inhabiting Madeira and Porto Santo, 108 are endemic Out of the 108, 28 are common to Madeira and the Azores. (List collated by Dr. Lemann, kindly communicated by Dr. Joseph Hooker.) In the Flora Azorica of Seubert, 400 (flowering and flowerless) plants are enumerated, of which 50 are stated to be endemic and peculiar to the Azores, 34 extra-European, including 23 common to the Azores and Madeira, or the Canaries, and 316 European. The Azorean researches of Mr. Hewett Watson (see his papers in the Botanical Magazine) add to and correct this list.

9. The termination of the Glacial epoch in Europe was marked by a recession of an Arctic fauna and flora northwards, and of a fauna and flora of the Mediterranean type southwards, and in the interspace thus produced, there appeared on land the general Germanic fauna and flora, and in the sea that fauna termed Celtic.

10. The causes which thus preceded the appearance of a new assemblage of organised beings, were the destruction of many species of animals and probably also of plants, either forms of extremely local distribution, or such as were not capable of enduring many changes of conditions—species, in short, with very limited capacity for horizontal or vertical diffusion.

11. All the changes before, during, and after the Glacial epoch, appear to have been gradual and not sudden, so that no marked line of demarcation can be drawn between the creatures inhabiting the same element and the same locality, during two proximate periods.