Page:Hardwicke's Science-Gossip - Volume 1.pdf/84

The Study of the Past History of Existing Species of Plants.—In a recent paper on the "Origin of the British Flora," it was suggested, in proof of its probable antiquity, that ligneous as well as herbaceous plants may have been preceded by numerous generations. If we confine our remarks to the existing species of oak, elm, maple, pine, yew, and cedar, some of which we know to have lived for hundreds of years, and, in the case of yew and cedar, from fifteen hundred to two thousand years—since inductive science is not able to make us understand extra-natural phenomena—we can only determine the probable number of generations which have preceded the birth of these monarchs of the forest, or their botanical dynasty, by an appeal to the testimony of the rocks. We know from the evidence of the rocks, that existing vegetation is only a continuation, through numerous geological changes, of an anterior vegetation. How long, then, have the existing species of oak, elm, maple, pine, yew, and cedar, been in existence? at what geological epoch were they introduced? and to what extinct species is their ancestry traceable? An attempt to answer these questions has yet to be made. Our most eminent living geologists—Lyell and Prestwich—will acknowledge as much. Very little has yet been done in quaternary geology by botanists, and what has been done seems to us to be most unsatisfactory. The question as to the successive epochs at which existing species have been made their appearance can only be determined by a careful study of the botanical remains found in, comparatively speaking, recent geological formations; and as leaves appear to be the most common forms in which these remains are found, in many instances the nervation being most beautifully preserved, it follows that the careful study of the nervation of the leaves of existing species is a very suitable preparation for these researches. As a means of enabling us to study the ramifications of the nerves in the leaf, the process of nature-printing offers us most invaluable aid. When we consider how exceedingly polymorphous the leaves are on most plants; how leaves, in the neighbourhood of the flower, lose their lobes, teeth, and other incisions, and take an entire edge, or lose their petiole and become sessile, sliding imperceptibly into bracts, and then into the sepals of the calyx, it must be obvious that in the case of vegetable remains, where leaves only are found, in determining a fossil plant from its leaf, we must fall back on characters more constant, and therefore more reliable. These characters are furnished by the nervation of the leaves. Unhappily, we have not at present any work in the English language in which a classification of the various types of leaves has been effected, founded on characters taken from their nervation. The only work to which we can refer the reader is an exceedingly expensive one, published by the Austrian government. In this work the Austrian flora has been copied by the nature-printing process. A separate work has also been published on the nervation of leaves. There is nothing to prevent such English botanists, whose neighbourhoods afford the necessary facilities, from working in this novel and deeply interesting field. We want a list of our living plants, and the relative ages of the geological formations in which they are found. The most recent beds are the most important, as bearing directly upon this question, as to the antiquity of the existing species of ligneous plants. We most earnestly call the attention of botanists to this subject, reminding them that, wherever a plant is found, whether on earth's surface or in its interior, it is legitimate botanizing territory. It is certain that nature is now preserving in modern lacustrine, fluviatile, and æstuarine deposits, specimens of existing species; we know that she has done so at former epochs, it is, therefore, apparent that it is only in these modern formations that the lost links will be discovered which unite the present with the former plant creations.

The Order of Succession in the Drift-beds of the Island of Arran.—At a meeting of the Geological Society (Jan. 25), Dr. J. Bryce read a paper on this subject. "In a paper read last year before the Royal Society of Edinburgh, the Rev. R. B. Watson described all these beds as boulder-clay, and did not assign the shells which he had discovered in them to any particular part of the deposit. Dr. Bryce dissented from this view, and in this paper pointed out the various causes of error likely to mislead an observer in examining such accumulations. He then described the various sections of the deposits, and showed that the lowest bed is a hard, tough, unstratified clay, full of striated, smoothed, and polished stones of all sizes, but totally devoid of fossils, and that it is, in fact, the true old boulder-clay of the geologists of the west of Scotland. The shells are entirely confined to a bed of clay of open texture, containing a few small stones; it rests immediately on the boulder-clay as above defined, and is succeeded by various drift-beds, consisting of seams of clay and sand intermingled, containing stones that are rarely striated, and without shells. Dr. Bryce then discussed the probable origin of these drifts, and the amount of depression which the land had sustained before the shell-bed was deposited over the boulder-clay, which he considered to have been formed by land-ice emanating from central snow-fields, and covering the whole surface of the country."—The Reader.

The Occurrence of Beds in the West of Scotland in the Position of the English Crag.—Dr. Bryce also read a paper on this subject at the same time and place as the last. "In consequence of the results arrived at from the investigation of the drift-beds of Arran, Dr. Bryce determined to examine all the recorded cases of fossils occurring in the boulder-clay, the Chapel Hall case having, however, been already undertaken by the Rev. H. W. Crosskey. The most celebrated case is that of the occurrence of elephant-remains at Kilmaurs, near Kilmarnock, in Ayrshire; and the author showed, from a section of the quarry exposed for the purpose by Mr. Turner, of Dean Castle, which corresponded exactly with one already furnished to him by an aged quarryman, that the elephant-remains, the reindeer's horn, and the shells, all occurred in beds below the boulder-clay, and not in that deposit, as has always been stated. The same conclusion was arrived at respecting the occurrence of elephant-remains at Airdrie and Bishop-briggs, and of reindeer's horn with shells at Croftamie; and the author concluded by discussing the question whether the fossils belong to the Upper Crag period, or merely indicate a downward extension of the Arctic fauna which characterizes the beds directly above the boulder-clay, as described in the last paper."