clay to the Lias, in the same order in which they are passed over by the Irmin Way, reaching the surface of the Lias at a depth of about 1000 feet. 16. The Great OOLITE AND STONESFIELD SLATE.-The Great Oolite of the Western Counties is a calcareous series, in which the well-known Bath Oolite is imbedded. As we trace this series towards the north-east, it becomes much modified, and the lower beds appear to pass into the celebrated Stonesfield Slate* (or tile-stone). Stonesfield, a small village near Woodstock, about twelve miles north-west of Oxford, has long been celebrated for the fossils imbedded in its thin-bedded limestone ; † bones and teeth of large reptiles and of fishes, and other remains from this locality, were described and figured by Lhwyd, more than a century ago.‡ Dr. Buckland's memoir on the great fossil reptile of Stonesfield, the Megalosaurus,§ where he at the same time mentioned the discovery of mammalian jaws in the same deposits, drew special attention to this interesting locality. The Stonesfield strata have been ascertained, by Mr. Lonsdale, to belong to the lower division of the Great Oolite; from Dr. Fitton's description of the circumstances under which they occur, we learn that in crossing the country from Oxford to Stonesfield, the Oxford clay with its characteristic fossils is first observed; this is succeeded by the Cornbrash-the uppermost stratum of the Great Oolite group, which is seen beneath the clay in several quarries on the sides of the road to Woodstock and Blenheim. . . . . The village of Stonesfield is situated on the brow of a valley, both sides of which are deeply excavated by the shafts * Phillips's Manual of Geology, p. 303. + Commonly called Stonesfield slate. As the term "slate " is technically applied to the old metamorphic clay-slates only, it is misapplied to the laminated rock of Stonesfield, which is fissile by its stratification, not by "cleavage." Lithophylacii Britannici Ichnographia. § Geological Transactions, second series, vol. i. p. 390. Zoological Journal, vol. iii. p. 416. and galleries that have been constructed for the extraction of the "slate." The beds that supply the stone are at a depth of about fifty feet below the summit, and are worked by shafts. The upper twenty-five feet consist of clays alternating with calcareous stone; the lower of fine-grained oolitic limestone, with numerous casts of shells. From the bottom of the shaft, drifts or horizontal excavations are made around, extending as far as safety will permit; the beds above being supported by piles of the less valuable materials. The strata thus worked do not exceed six feet in thickness; they consist of sandy beds imbedding large calcareous concretions, which, by exposure to the frost, admit of separation into thin flakes. Fissile calcareous concretions, similar to those of Stonesfield, occur also at Wittering and Collyweston, associated with sandy beds and oolite limestones, and contain ferns and other terrestrial plants, together with marine shells. 17. ORGANIC REMAINS OF THE STONESFIELD SLATE.The majority of the fossils of Stonesfield, although of so highly interesting a character, have hitherto been very imperfectly investigated. The vegetable remains consist of fucoidal plants, and of palms, arborescent ferns, and plants allied to the Zamia and Cycas, with seed-vessels, leaves, and stems of coniferæ, and traces of reed-like plants. The shells are jurassic in their character; and one small bivalve (Trigonia impressa) is extremely abundant. The bones and teeth of the gigantic terrestrial reptile related to the Monitor, the Megalosaurus, mentioned above as occurring in the Wealden (vol. i. p. 435), bones of Pterodactyles or flying lizards, bones and plates of Turtles, and other osseous remains, apparently of saurians, present a striking general correspondence with the fossils of the Wealden. The elytra or wing-cases of beetles, and other relics of insects, are of frequent occurrence. The teeth, scales, fin-bones, and rays of fishes belong for the most part to the same genera and species as those contained in other jurassic strata; teeth of Lepidotus and Hybodus are frequently met with; but * * See Buckland's Bridgwater Treatise for figures of several fossils from Stonesfield. by far the most interesting fossils are the mammalian remains. 18. FOSSIL MAMMALIA OF STONESFIELD.*-The lamin ated oolitic limestones of Stonesfield have yielded some of the most precious relics of the past ages of our globe-most 2 1 LIGN. 120.-THE RIGHT SIDE OF THE LOWER JAW OF A MARSUPIAL MAMMALIAN; STONESFIELD. (From Zoolog. Journ. vol. iii. pl. xi.) Fig. 1. Natural size. Fig. 2. Enlarged view of a single tooth. (Phascolotherium Bucklandi).† of the known vestiges of mammalian animals in the secondary formations, in other words, in deposits of an age *See Prof. Owen's Memoir in the Geol. Trans. 2 ser. vol. ii. p. 147; Medals of Creation, vol. ii. p. 805; Petrifactions, p. 401. †The original is in the British Museum; it is in an admirable state of preservation; and the piece of rock in which it is imbedded has numerous casts of the Trigonia impressa, which occur in such profusion in the Stonesfield tilestone. Emmons's Dromatherium, from the Chatham Coal-field of North Carolina, and Plieninger's Microlestes, from the Wirtemberg Bone-bed, are Mammalia of still more ancient date. long antecedent to the mammaliferous eocene epoch :—a fact of the highest interest to the geologist, since it carries back the existence of the higher vertebrated animals to a period of unfathomable antiquity. The mammalian remains hitherto discovered comprise, firstly, a portion of lower jaw, with teeth, of a small pachydermatous animal (the Stereognathus),* nearly related to some of the Eocene mammals, such as the Hyracotherium and Pliolophus; † and, secondly, at least seven specimens of portions of lower jaws, with teeth, belonging to very small animals, and referable to two genera. One of these is allied to the Wombat (Phascolomys), a marsupial animal of New South Wales; proving that the remarkable character of the mammalian fauna of Australia also prevailed in a very remote period, and that it is not, as some have inferred, a new order of things. The other was a small insectivorous mammal (Amphitherium), having thirty-two teeth in the lower jaw; its marsupial affinities are doubtful.‡ 19. COMPARISON OF THE STONESFIELD AND WEALDEN FOSSILS.-We have seen that the zoological characters of the Oolite and Lias are decidedly marine, with intercalations of materials brought down by rivers into the sea, and transported by currents to a more or less distant part of the oceanic basin. Unlike the organic remains of the Wealden, the terrestrial and fresh-water productions are mingled with marine plants, shells, and fishes. Thus, while the Chalk consists of the bed of a deep sea with scarcely any intermixture either of land or fresh-water debris, and the Wealden of a delta in which but few marine exuviæ are imbedded, the Lower Oolitic series presents an intermediate character, of which the Stonesfield strata afford a highly interesting ex * Quart. Journ. Geol. Soc. vol. xiii. p. 1. + Described by Prof. Owen in Geol. Proceed. for May 20, 1857. In Prof. Owen's "British Fossil Mammals," are exquisite figures and an elaborate philosophical notice of the mammalian remains discovered in the "Stonesfield slate." See also Lyell's Manual, p. 312. ample. The reader cannot fail to mark the general correspondence that exists between the organic remains imbedded in these fluvio-marine deposits of the Oolite and those of the Wealden: * the following tabular view will render this analogy more obvious Wealden and Purbeck Strata. Stonesfield and Collyweston Slates. Drifted coniferous wood and lig- Drifted coniferous wood. nite. Equiseta. Fucoidal plants. Ferns: Sphenopteris, Lonchopte- Ferns: Sphenopteris, Taniopteris, ris, &c. Cycadaceæ. &c. Cycadaceæ. Carpolithes, and undetermined Carpolithes, and seed-vessels. seed-vessels. Fresh-water shells: Paludina, Cy- Marine shells clas, Unio, &c. Freshwater Crustaceans: Cypridæ. gonia, &c. undetermined Marine Crustaceans: Astacidæ, &c. Fishes of the genera Hybodus, Le- Fishes of the genera Hybodus, Le : terrestrial Megalosaurus, Megalosaurus. Hylæosaurus, Iguanodon, &c. Crocodilian-Goniophilis, Poecilo- Teleosaurus. pleuron, &c. Pterodactyles. Birds? Pterodactyles. Birds? MAMMALIA: several genera (Pur- MAMMALIA: three genera. beck). From this table we perceive at a glance, that the fauna and flora of the dry land during the deposition of the Stonesfield oolite and the Wealden-strata were essentially the same; while the difference in the mollusca points out the respective conditions under which the deposits took * See also Fossils of the South Downs, &c. 1822, p. 37 and 59. |