air like the Ichthyosaurus and our modern Cetacea. Some of the reptiles above mentioned were of formidable dimensions. One skeleton of Ichthyosaurus platyodon, from the Lias at Lyme, now in the British Museum, must have belonged to an animal more than 24 feet in length; and there are species of Plesiosaurus which measure from 18 to 20 feet in length. The form of the Ichthyosaurus may have fitted it to cut through the waves like the porpoise; as it was furnished, besides its paddles, with a tail-fin so constructed as to be a. powerful organ of motion; but it is supposed that the Plesiosaurus, at least the long-necked species, was better suited to fish in shallow creeks and bays defended from heavy breakers. It is now very generally agreed that these extinct saurians must have inhabited the sea. There are modern examples of marine reptiles. The common crocodile of the Ganges is well known to frequent equally that river and the brackish and salt water near its mouth; and crocodiles are said in like manner to be abundant both in the rivers of the Isla de Pinos (or Isle of Pines), south of Cuba, and in the open sea round the coast. In 1835 a curious lizard (Amblyrhynchus cristatus) was discovered by Mr. Darwin in the Galapagos Islands. It was found to be exclusively marine, swimming easily by means of its flattened tail, and subsisting chiefly on seaweed. One of them was sunk from the ship by a heavy weight, and on being drawn up, after an hour, was quite unharmed. The families of Dinosauria, Crocodilia, and Pterosauria or winged reptiles, are also represented in the Lias. Sudden destruction of Saurians.-It has been remarked, and truly, that many of the fish and saurians, found fossil in the Lias, must have met with sudden death and immediate burial; and that the destructive operation, whatever may have been its nature, was often repeated. Sometimes,' says Dr. Buckland, 'scarcely a single bone or scale has been removed from the place it occupied during life; which could not have happened had the uncovered bodies of these saurians been left, even for a few hours, exposed to putrefaction, and to the attacks of fishes and other smaller animals at the bottom of the sea.' Not only are the skeletons of the Ichthyosaurs entire, but sometimes the contents of their stomachs still remain between their ribs, as before remarked, so that we can discover the form of their excrements and the 7 Conybeare and De la Beche, 8 See Darwin, Naturalist's Voyage. Geol. Trans. First Series, vol. v. p. p. 385. Murray. 559; and Buckland, Bridgewater Treatise, p. 203. Y Bridgewater Treatise, p. 115. particular species of fish on which they lived. Not unfrequently there are layers of these coprolites, at different depths in the Lias, at a distance from any entire skeletons of the marine lizards from which they were derived; 'as if,' says Sir H. de la Beche, the muddy bottom of the sea received small sudden accessions of matter from time to time, covering up the coprolites and other exuvia which had accumulated during the intervals.' It is further stated that, at Lyme Regis, thosesurfaces only of the coprolites which lay uppermost at the bottom of the sea have suffered partial decay from the action of water before they were covered and protected by the muddy sediment that has afterwards permanently enveloped them. Numerous specimens of a kind of Calamary (Geoteuthis Bollensis) have also been met with in the Lower Lias at Lyme, with the ink-bags still distended, containing the ink in a dried state, chiefly composed of carbon, and but slightly impregnated with carbonate of lime. These dibranchiate Cephalopoda, therefore, must, like the saurians, have been soon buried in sediment; for, if long exposed after death, the membrane containing the ink would have decayed.2 As we know that river-fish are sometimes stifled, even in their own element, by muddy water during floods, it cannot be doubted that the periodical discharge of large bodies of turbid fresh water into the sea may be still more fatal to marine tribes. In the Principles of Geology' I have shown that large quantities of mud and drowned animals have been swept down into the sea by rivers during earthquakes, as in Java in 1699; and that indescribable multitudes of dead fishes have been seen floating on the sea after a discharge of noxious vapours during similar convulsions. But in the intervals between such catastrophes, strata may have accumulated slowly in the sea of the Lias, some being formed chiefly of one description of shell, such as Ammonites, others of Gryphites. Corals, rare in the Upper and Middle Lias, become frequent in some of the lowest deposits of the Infra-lias, as at Brocastle and Southerndown in South Wales. This group represents the Hettangian of continental geologists. Freshwater deposits—Insect-beds. From the above remarks, the reader will infer that the Lias is for the most part a marine deposit. Some members, however, of the series have an estuarine character, and must have been formed within the influence of rivers. At the base of the Upper and Lower Lias respectively, insect-beds appear to be almost everywhere 1 Geological Researches, p. 334. 2 Buckland, Bridgewater Treatise, p. 307. 3 Fig. 383. Nat. size. Wing of a neuropterous insect, from present, throughout the Midland and South-western districts of England. These beds are crowded with the remains of insects, small fish, and crustaceans, with occasional marine shells. One band in Gloucestershire, rarely exceeding a foot in thickness, has been named the insect limestone.' It passes upwards, says the Rev. P. B. Brodie, into a shale containing Cypris and Estheria, and is full of the wing-cases of several genera of Coleoptera, with some nearly entire beetles, of which the eyes are preserved. The nervures of the wings of neuropterous insects (fig. 383) are beautifully perfect in this bed. Ferns, with Cycads and leaves of monocotyledonous plants, and some apparently brackish and freshwater shells, accompany the insects in several places, while in others marine shells predominate, the fossils varying apparently as we examine the bed nearer or farther from the ancient land, or the source whence the fresh water was derived. After studying 300 specimens of these insects from the Lias, Mr. Westwood declares that they comprise both wood-eating and herb-devouring beetles, of the genera Elater, Carabus, &c., besides grasshoppers (Gryllus), and detached wings of dragon-flies and may-flies, or insects referable to the genera Libellula, Ephemera, Hemerobius, and Panorpa. The size of the species is usually small, and such as, taken alone, would imply a temperate climate; but many of the associated organic remains of other classes must lead to a different conclusion. At Schambelen, in the canton of Argovia in Switzerland, a rich insect fauna has been brought to light agreeing in general character with the insect-beds of England, but comprising nearly three times the number of species in a very perfect state. Fossil plants.-Among the vegetable remains of the Lias, several species of Cycads of the genus Palæozamia have been found at Lyme Regis, and the remains of coniferous plants at Whitby, of the genera Pinites, Cupressus and Peuce. M. Ad. Brongniart enumerates forty-seven liassic Acrogens, most of them ferns; and fifty Gymnosperms, of which thirty-nine are Cycads and eleven Conifer. Among the Cycads the predominance of Zamites, and among the ferns the numerous genera with leaves having reticulated veins (as in fig. 351), are mentioned as botanical characteristics of this era.1 The absence as yet 4 Tableau des Vég. Foss. 1849 A History of Fossil Insects, &c. 1846. London. p. 105. from the Lias and Oolite of all signs of Dicotyledonous Angiosperms is worthy of notice. Amongst the genera of ferns are Otopteris, and Alethopteris; and Equisetetes are also found. Origin of the Oolite and Lias.-The entire group of Oolite and Lias consists of repeated alternations of strata of clay, sandstone, and limestone, following each other in the same order. Thus the clays of the Lias are, in ascending order, followed by the Midford sands, and these by the shelly oolitic and pisolitic beds of the Inferior Oolite, succeeded by the oolitic limestone called the Great or Bath Oolite. So, in the Middle Oolite, the Oxford clay is followed by calcareous grit and coral rag; lastly, in the Upper Oolite, the Kimmeridge clay is followed by the Portland sand and limestone." The clay beds, however, as Sir H. de la Beche remarks, can be followed over larger areas than the sand or sandstones. Arenaceous deposits occur with coal and lignite in Yorkshire and Scotland, and resemble a coalfield. In the Alps the strata assume an almost purely calcareous form, the sands and clays being omitted. In some Oolitic districts the clays and intervening limestones retain a uniform character, for distances of from 400 to 600 miles from east to west and north to south. In order to account for such a succession of strata, we may imagine the bed of the ocean to be at first the receptacle for ages of fine argillaceous sediment, brought by oceanic currents, which may have communicated with rivers, or with part of the sea near a wasting coast. This mud ceases, at length, to be conveyed to the same region, either because the land which had previously suffered denudation is depressed and submerged, or because the current is deflected in another direction by the altered shape of the bed of the ocean and neighbouring dry land. By such changes the water becomes once more clear and fit for the growth of stony zoophytes. Calcareous sand, oolite and pisolite are then formed from comminuted shell and coral, or, in some cases, arenaceous matter replaces the clay; because it commonly happens that the finer sediment, being first drifted farthest from coasts, is subsequently overspread by coarse sand, after the sea has grown shallower, or when the land increasing in extent, whether by upheaval or by sediment filling up parts of the sea, has approached nearer to the spots first occupied by fine mud. The increased thickness of the limestones in those regions, as in the Alps and Jura, where the clays are comparatively thin, arises from the calcareous matter having been derived from 5 Conybeare and Philips' Outlines, &c. p. 166. 6 Geological Researches, p. 337. species of corals and other organic beings which lived in clear water, far from land, to the growth of which the influx of mud would be unfavourable. Portions, therefore, of these clays and limestones have probably been formed contemporaneously to a greater extent than we can generally prove, for the distinctness of the species of organic beings would be caused by the difference of conditions between the more littoral and the more pelagic areas and the different depths and nature of the seabottom. Independently of those ascending and descending movements which have given rise to the superposition of the limestones and clays, and by which the position of land and sea are made in the course of ages to vary, the geologist has the difficult task of allowing for the contemporaneous thinning out in one direction and thickening in another, of the successive organic and inorganic deposits of the same era. On the whole, the Oolitic age was one of slow subsidence over vast areas. The Lias is well represented in the north and north-west of France, and the British subdivisions occur there. In addition, the equivalents of the Sutton stone and Brocastle deposits, the Hettangian, are well developed, and have a great fauna. This Infra-lias rests conformably on the zone of Avicula contorta. In Switzerland, important insect-beds occur, and in Germany the succession resembles that of England. CHAPTER XXII. TRIAS, OR NEW RED SANDSTONE Group. Beds of passage between the Lias and Trias, Rhætic beds and mammifer -Triple division of the Trias Keuper, or Upper Trias of EnglandReptiles of the Upper Trias-Footprints in the Bunter formation in England-Dolomitic conglomerate of Bristol-Origin of Red Sandstone and Rock-salt-Precipitation of salt from inland lakes and lagoonsTrias of Germany-Succession-Keuper-St. Cassian and Hallstadt beds -Peculiarity of their fauna-Muschelkalk and its fossils-Trias of the United States-Fossil footprints of birds and reptiles in the valley of the Connecticut-Triassic mammifer of North Carolina-Triassic coal-field of Richmond, Virginia-Indian Trias-The break at the base. Beds of passage between the Lias and Trias-Rhætic beds. We have mentioned in the last chapter (p. 315) that the base of the Lower Lias is characterised, both in England and Germany, by beds containing distinct species of Ammonites, the lowest subdivision having been called the zone of Ammonites planorbis. Below this zone, on the boundary line between the Lias |