It is easy to see that similar difficulties beset every attempt to trace the development of plants on the principle of slow and gradual evolution, and we are driven back on the theory of periods of rapid origin, as we have already seen suggested by Saporta in the case of the Cretaceous dicotyledons. Such abrupt and plentiful introduction of species over large areas at the same time, by whatever cause effected—and we are at present quite ignorant of any secondary causes—becomes in effect something not unlike the old and familiar idea of creation. Science must indeed always be baffled by questions of ultimate origin, and, however far it may be able to trace the chain of secondary causation and development, must at length find itself in the presence of the great Creative Mind, who is “before all things and in whom all things consist.”
I.—COMPARATIVE VIEW OF THE SUCCESSIVE PALÆOZOIC
FLORAS OF NORTHEASTERN AMERICA AND
GREAT BRITAIN.
In eastern Canada there is a very complete series of fossil plants, extending from the Silurian to the Permian, and intermediate in its species between the floras of interior America and of Europe. I may use this succession, mainly worked out by myself,[FG] to summarise the various Palæozoic floras and sub-floras, in order to give a condensed view of this portion of the history of the vegetable kingdom, and to direct attention to the important fact, too often overlooked, that there is a definite succession of fossil plants as well as of animals, and that this is important as a means of determining geological horizons. A British list for comparison has been kindly prepared for me by Mr. R. Kidston, F. Gr. S. For lists referring to the western and southern portions of America, I may refer to the reports of Lesquereux and Fontaine and White.[FH]
[FG] “Acadian Geology,” “Reports on Fossil Plants of Canada,” Geological Survey of Canada.
[FH] “Geological Surveys of Pennsylvania, Ohio, and Illinois.”
In this connection I am reminded, by an excellent little paper of M. Zeiller,[FI] on Carboniferous plants from the region of the Zambesi, in Africa, that the flora which in the Carboniferous period extended over the temperate portions of the northern hemisphere and far into the arctic, also passed across the equator and prevailed in the southern hemisphere. Of eleven species brought from the Zambesi by M. Lapierre and examined by M. Zeiller, all were identical with European species of the upper coal-formation, and the same fact has been observed in the coal flora of the Cape Colony.[FJ] These facts bear testimony to the remarkable uniformity of climate and vegetation in the coal period, and I perfectly agree with Zeiller that they show, when taken in connection with other parallelisms in fossils, an actual contemporaneousness of the coal flora over the whole world.
[FI] Paris, 1883.