Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/362

Rh of the type now known as Mediterranean, extended far into the Atlantic—past the Azores—and that, in all probability, the great semicircular belt of gulf-weed ranging between the 15th and 45th degrees of north latitude, and constant in its place, marks the position of the coast-line of that ancient land, and had its parentage on its solid bounds. The following extract from the writings of one of the first of living algologists, Will show that there are botanical grounds for my speculation respecting the gulf-weed.

"Authors who have written on this Fucus have much disputed, both respecting its origin, and whether it continues to grow whilst floating about. Nothing at all bearing on the former question has yet been discoyered; for though species of Sargassum abound along the shores of tropical countries, none exactly corresponds with S. bacciferum. That the ancestors of the present bank have originally migrated from some fixed station, is probable; but further than probability we can say nothing. That it continues to flourish and gprow in its present situation is most certain. Whoever has picked it up at sea, and examined it with any common attention, must have perceived, not only that the plants were in vigorous life, but that new fronds were continually pushing out from the old, the limit being most clearly defined by the colour, which, in the old frond, is foxy-brown; in the young shoots pale, transparent olive. But how is it propagated; for it never produces fructification? It appears to me, that it is by breakage. The old frond, which is exceedingly brittle, is broken by accident and the branches, continuing to live, push out young shoots from all sides. Many minute pieces that I have exa-mined, were as vigorous as those of larger size, but they were certainly not seedlings, and appeared to me to be broken branches, all having a piece of old frond from which the young shoots sprung. As the plant increases in size, it takes something of a globular figure, from the branches issuing in all directions, as from a centre. On our own shores we have two species analogous to S. bacciferum in their mode of growth, namely, Fukus Mackayi, and the variety B. sub-scostatus of Fucus vesiculosus (F. balticus, Ag.). Neither of these has ever yet been found attached, though they often occur in immense strata; the one, on the muddy sea-shore, the other, in salt marshes, in which situations, respectively, they continue to grow and flourish; and it is remarkable, that neither has ever yet been found in fructification, in which respect, also, they strikingly coincide with S. bacciferum. And if it be hereafter shown that F. Mackayi is merely F. nodosus, altered by gprowing under peculiar circumstances, may it not be inferred that Sargassum bacciferum,—which differs about as much from Sargassum vulgare as Fucus Mackayi does from Fucus nodosus—is merely a pelagic variety of that variable plant?"—Harvey, Manual of the British Algæ. (1841.) Introduction, pp. xvi. xvii.

My friend and colleague, Dr. Joseph Hooker, who has had great opportunities of studying the gulf-weed, believes with Dr. Harvey, that the Sargassum bacciferum is an abnormal condition of Sargassum vulgare. Now as the latter is essentially a coast-line plant, growing on rocks with a very limited vertical range, I propose to account for its abnormal condition as Sargassum bacciferum in the gulf-weed bank on the supposition of the submergence of the ancient line of coast on which it originated. Over this land that flora, of which we have now a few fragments in the west of Ireland, might with facility have migrated. This would give us a new antidate, and enables us to declare our entire existing terrestrial flora and fauna as post-miocene.

The fact that there is a well-marked belt of miocene coast-line in North America (as shown by Mr. Lyell), and that the mollusca of that belt, as I have convinced myself from personal examination, indicate a representatiye, not identical, fauna in that region proves that during the miocene period there was an Atlantic gulf separating the new world