GIDEON ALGERNON MANTELL, LL.D., F.R. S., F.G. S., SEVENTH EDITION, REVISED AND AUGMENTED, IN TWO VOLUMES.-VOL. II. LONDON: HENRY G. BOHN, YORK STREET, COVENT GARDEN. MDCCCLVIII. Edue T 20 9 7 8 2027 8.50.550 HARVARD COLLEGE LINKANY f&B 12 1932 36051.52 JOHN CHILDS AND SON, PRINTERS. PREFACE TO VOL. II. THE few months that have elapsed since the preparation and publication of the 1st volume of this edition of Mantell's "Wonders of Geology" have been as productive of geological facts and theories as any such former period, if not more so. Most of the new discoveries in geology, and of the determination or correction of former hypotheses, have been described or commented upon in various communications published by the Geological Society of London; and many other points of geological interest have been treated of in papers read before the Geological Societies of Dublin, Paris, Berlin, and Vienna, or before other Scientific Societies of Europe and America. Not to dwell upon the much-increased list of the planetoids (p. 44), to the known number of which seven have been already added,—or the additional recorded instances of aerolitic phenomena, but to refer to circumstances more closely connected with physical geology, we may draw attention to Sir C. Lyell's lucid résumé of facts relative to the secular elevation of the land,—of an abstract of a lecture on this subject not long since delivered, by the author of the "Principles," we have availed ourselves (p. 958). In another direction, our study of physical geology has of late been greatly aided by Mr. H. C. Sorby's remarkable researches in the microscopical structure of rocks, both sedimentary and hypogene, and of the component crystals of the latter (see p. 948). Mr. Prestwich's hypothetical extension of Upper Tertiary deposits over a great part of the South-east of England demands careful attention; and, though not yet clearly substantiated, and indeed still forming a geological problem difficult of solution, has already been productive of valuable results, in setting geologists at work again over a country once thought to have been nearly exhausted of geological novelties. But perhaps the discovery of a large granitic boulder in the heart of the Chalk of Croydon (p. 972) has been as prolific a source of geologic argument and romance as any fact lately brought forward. The outlines of the old cretaceous ocean and its archipelagos,-its shores and sea-deeps, its sea-weeds and drifted shells,-the jungles of its coasts,and the possible icebergs of its northern limits, offer a wide field both for the strict physicist and the imaginative geologist. With this subject is closely connected the probable existence in the early part of the Cretaceous period of a ridge of rocks, chiefly belonging to the coal-measures, ranging across the South British area, as explained and illustrated of late by Mr. Godwin-Austen (see p. 756, note). The presence of this old ridge in the cretaceous ocean has had two important results. In the first place it gave rise to local shingly deposits, interrupting the general succession of the sands and clays older than the Gault, and has thereby rendered it unlikely that we shall be able to obtain from beneath London such a supply of water, by means of very deep Artesian wells, as has been obtained at Grenelle from the Lower Greensand; and, secondly, it has probably borne up, as a part of its constituent mass, some coal-beds, continuous with those of Belgium on one hand, and of Somersetshire on the other; thereby possibly affording coal in deep borings, in this district. In the study of fossils, so many new and interesting facts have been elucidated, that we can only refer to a few: such as Mr. Beckles's further discoveries among the Mammalia and Reptilia of the Purbeck period, and his discovery of the bones of the entire foot of the Iguanodon, which, being three-toed, may well fit some of the fossil foot-marks de scribed at p. 383, as having been found in deposits formed among the haunts of this great reptile ;-to the descriptions, by Prof. Huxley and Mr. Kirkby, of Crustaceans of higher rank than Entomostraca in the Permian and Carboniferous deposits; to the discovery, by the geologists of Ludlow and the neighbourhood, of many more fish-remains in the Upper Silurian than had hitherto been known;-and especially to Dr. Falconer's luminous exposition of the zoological and geological relations of the true species of Mastodon and Elephant (see p. 963). To the results of Sir R. I. Murchison's well-sustained researches among palæozoic rocks and fossils we owe very much indeed that is new in our knowledge of the Permian and Silurian formations. Of the latter especially we have a recently corrected classification, which, elaborated by this distinguished geologist, and enriched by the labours of American, European, and British palæontologists, is, with Sir Roderick's kind permission, brought forward in this little work for the use of the student, even before its appearance in the forthcoming Second Edition of Sir R. Murchison's "Siluria." Last, not least, we must particularly notice the disentanglement of the ravelled clue to a clear knowledge of the relations of the rocks of Sutherlandshire, where Mr. Peach's late discovery of an important set of fossils in a band of altered limestone has enabled Sir R. Murchison to bring to their true bearings the observations made in this locality by himself and others, and not only to rectify errors and to disperse the obscurity which covered the geological. history of the North-western Highlands of Scotland, but to place enormous masses of the stratified rocks of this region into their right places in the geological scale, and in relation with their equivalent formations in Scandinavia, Canada, Wales, and elsewhere. February, 1858. T. RUPERT JONES. |