CHAPTER XVI. ON THE LOWER OR MORE ANCIENT TERTIARY STRATA. Formation of Tertiary Strata in Lakes or Inland Seas.-Lakes of North America. Falls of Niagara.-Alternations of Marine and Fresh water Strata.-Arrangement of the Tertiary Strata in the Paris Basin.-Plastic Clay and London Clay-Geology of the lower Vale of the Thames.-Remains of Crocodiles and the Nautilus in London Clay.-Molasse of Alpnach in Switzerland, with Coal and Teeth of the Mastodon.-Calcaire Grossier, or Coarse Limestone of the Paris Basin, supposed to be of the same Age as the London Clay.-Calcaire Silicieux.-Gypsum and Gypseous Marl of the Paris Basin, containing Bones of numerous extinct Species of Land Quadrupeds.-Remarks on their discovery and Organization by Baron Cuvier.-Marine Sandstone.-Millstone.-Upper Freshwater Formation.-Tertiary Strata in the Isle of Wight.-Crag of Norfolk, its true Geological Position not determined.-Cliffs of Brighton. The name of tertiary has been given with much propriety to all the strata that are more recent than the secondary; the term is intelligible, and ought not to be changed without sufficient reason; the introduction of new names in science serves only to perplex the student, and is attended with no advantage. The name of supercretaceous, which has recently been applied to the tertiary strata, is peculiarly inappropriate, as these strata may cover any of the lower rocks, and in Auvergne they may be seen resting on granite. If a new name were necessary, post-cretaceous should have been chosen; as all geologists are agreed, that the tertiary strata were deposited after chalk. THE tertiary formations comprise all the regular strata of limestone, marl, clay and sandstone, that have been deposited after chalk. It is only since the commencement of the present century that they have attracted the notice of geologists: their true nature was before unknown, or they were supposed to be local and alluvial depositions. It is now discovered that tertiary formations are widely spread over many parts of the globe, and are often of considerable thickness. The first circumstance which proved that the tertiary beds were distinct from the secondary, was the discovery that many of these beds contain the bones of the higher order of animals, as perfect in their organization as any of the existing species of land quadrupeds. The tertiary beds were farther remarkable, for presenting frequent alternations of beds, containing the remains of marine animals, with other beds that contain exclusively the remains of land animals, and plants, and fresh water shells: hence the latter beds were denominated fresh water formations. A more accurate examination of the secondary strata, has since been discovered, that fresh water formations occur also among the more ancient strata, but their characters are not so distinctly marked. When the first edition of this work was published, viz. early in 1813, the name of freshwater formations was scarcely known in England, but the author ventured to of fer an explanation of their formation, from what is now taking place in extensive lakes a similar explanation has since been generally adopted. "The lakes of North America, are seas of fresh water, more than 1500 miles in circuit; they are placed at a considerable elevation above the Atlantic, and at different levels. They unite by small straits or rivers, which have a rapid descent. On some of the rivers are prodigious waterfalls, which are continually enlarging and deepening the passage from one to the other; and will ultimately effect the drainage of the upper lakes. The falls of Niagara, are well known; the water is divided by a small island, which separates the river into two cataracts, one of which is 600 yards, and the other 350 yards wide: the height of the fall is from 140 to 160 feet. It is estimated that 670,000 tons of water are dashed every minute with inconceivable force, against the bottom, and are thus wearing down the adjacent rocks. Since the banks of the cataract were inhabited by Europeans, they have observed that it is progressively shortening the distance of the falls from Lake Erie. When it has worn down the intervening calcareous rocks, the upper lake will become dry land, and form an extensive plain or valley, surrounded by rising ground, and watered by a river or smaller lake, which will Occupy the lowest part. In this plain future geologists may trace successive strata of fresh water formation, covering the subjacent ancient limestone. The gradual deposition of minute earthy particles, or the more rapid subsidence of mud from sudden inundations, will form distinct beds, in which will be found the remains of freshwater fish, vegetables and quadrupeds."-1st edition, 1813, pp. 182, 183. In the frontispiece to the present volume will be seen a bird's-eye view, or map of the country round Niagara, drawn by my eldest son, who passed several days at the falls of Niagara in 1830. In this drawing the accurate proportion of distance is disregarded, in order to bring the several objects into one point of view. The deep chasm formed by the cataract is seen in front, from which the water is issuing into a lower country at Lewiston, nearly on a level with Lake Ontario, into which the river flows. Mr. Joseph Henry, in a topographical sketch of the state of New York, says, "The descent of the country from Lake Erie to Ontario is principally by a step, not at the falls, but at Lewiston, several miles below:" this is the position from which the drawing in the frontispiece was taken. Mr. H. adds, "In viewing the position of the falls, and the features of the country round, it is impossible not to be impressed with the idea, that this great natural race-way has been formed by the continued action of the irresistible current of the Niagara, and that the falls, beginning at Lewiston, have, in the course of ages, worn back the rocky strata to their present site. The deep chasm through which the Niagara passes, below the falls, is nearly a mile wide with almost perfect mural sides."-Transactions of the Albany Institute. In Mr. Loudon's Magazine of Natural History, March, 1830, there is an account of the falls of Niagara, and of the physical structure of the adjacent country, by my son, Robert Bakewell, junior. I preferred making the above extract from Mr. Henry's description, as it confirms the general accuracy of the drawing in the frontispiece. Below will be seen a statement of the levels and the extent of the North American lakes.* These lakes may justly be styled seas of fresh water. Though their present surface is considerably elevated above the level of the ocean, the bottom of some of the largest lakes is much below the tide line; and were these lakes situated nearer to the Atlantic, we might easily imagine that after the fresh water had subsided to the sea level, they might be subject to frequent irruptions of salt water, which would produce a change in the nature of the inhabitants of these lakes; or, in other words, would occasion alternations of marine with freshwater strata, without any change in the relative level of the land and sea. In England and France, there appears to have been a considerable interval between the deposition of the chalk, and of the lowest beds of the secondary strata; for the surface of the chalk is deeply furrowed and broken, apparently by the action of torrents, or inundations, and the hollows filled by the tertiary beds. In some parts of the Continent, however, the line of separation between the secondary and tertiary strata is not so distinctly marked, and they are both elevated together, conformably. The tertiary strata form the outer crust of the globe, and have, every where, been subjected to erosion from torrents and inundations, that have swept over parts of its surface, and transported the fragments into distant countries or into the ocean. We cannot, from the present localities of the upper strata, determine, with any precision, the boundaries of the inland lakes or seas in which they were deposited. Many of these strata have, evidently, once extended far beyond their present limits; but have been so completely destroyed, that we can infer their former existence, only by a few remaining detached portions. * From Lake Erie to the falls of Niagara, the distance is 21 miles. From the falls to Lewiston, at the mouth of the chasm, the distance is 7 miles. From Lewiston to Lake Ontario the distance is 7 miles. Total quantity of square miles covered by the lakes, 72,930. In France, the tertiary strata are more widely spread, and many of them more fully developed, than in England: it is indeed scarcely possible to imagine a more distinct display of the series of strata in any class of rocks, than is presented, close to the very gates of Paris. In a capital so distinguished for scientific investigation, and possessing so many able and acute observers, it does, indeed, seem extraordinary, that the strata with which they were surrounded, should never have been properly examined until so recent a period, as the early part of the present century. What is daily before our eyes seldom excites attention, or is deemed deserving of much notice; but there was another cause which long prevented the philosophers of Paris from observing the remarkable objects around them. Captivated with the generalizations of Werner, who, it was firmly believed, had unlocked all the hidden mysteries of geology, and comprised in his system all the different formations that composed the crust of the globe, they saw before them a series of strata which had no agreement with any part of the Wernerian classification; hence, they could not avoid the painful persuasion, either that the system of Werner was incomplete, or that they were unable to apply it properly. To avoid an acknowledgment so little satisfactory, the geologists of Paris averted their attention, and that of their pupils, from nearer objects, and directed them to the mountains of Germany or Switzerland. Had not another science (comparative anatomy) come to the aid of geology, we might yet have remained unacquainted with the tertiary strata around Paris. At length, the number of skeletons of strange and unknown animals discovered in some of the strata, forcibly attracted the notice of that distinguished naturalist, Cuvier, and it was resolved to investigate attentively the geology of the whole district. M. A. Brongniart was associated with Cuvier in the investigation; and in 1811 the result of their labours and observations was given, in a work entitled Essai sur la Géographie Minéralogique des Environs de Paris,-the most luminous and interesting exposition of local geology ever presented to the world; and from this period we may date the first accurate knowledge of the tertiary strata. The following extract from the Essay of MM. Cuvier and Brongniart, presents a general view of the arrangement of the strata round Paris: "The country in which the capital of France is situated, is perhaps the most remarkable that has yet been observed, both from the succession of different soils of which it is formed, and from the extraordinary organic remains which it contains. Millions of marine shells, which alternate regularly with freshwater shells, compose the principal mass. Bones of land animals, of which the genera are entirely unknown, are found in certain parts; other bones remarkable for their vast size, and of which some of similar genera (quelques congenères) exist only in distant countries, are found scattered in the upper beds. A marked character of a great irruption from the south-east is impressed on the summits (caps), and in the direction of the principal hills. In one word, no country can afford more instruction respecting the last revolutions, which have terminated the formation of the present continents." Though chalk is the foundation rock of the country, for a considerable extent round Paris, being covered by tertiary strata, it rises to the surface only in a few situations. The total thickness of the tertiary strata over the chalk, as given in an ideal section of the country, is nearly five hundred feet.* Many of the tertiary beds in the Paris basin are not found elsewhere, and therefore cannot be taken as types of other tertiary formations; and the lower bed, called the plastic clay, is but very imperfectly developed near Paris. In attempting to generalize the tertiary formations, a difficulty presents itself, if we are to class them by their zoological characters; for some of the formations, which in certain situations, contain, exclusively, the remains of marine animals, present, in other places, river or lake shells, with wood and the bones of land animals. It is, therefore, probable, that while the waters in one lake or basin might be saline, those in another lake might be fresh; and two cotemporaneous formations may hence contain very different organic remains. The tertiary strata in England and in the north of France, may be arranged under four divisions, which are given below: after describing these, the more recent tertiary strata, called by some French geologists Quaternary, will be noticed in the following Chapter. The following ascending series of beds of the Paris basin was first given as a correct account of their succession: more extended observations have proved that the position of No. 3, or the Calcaire siliceux, is higher in the series. 1. Plastic Clay and Lower Sand. 2. Calcaire grossier. 3. Calcaire siliceux and Sandstone. 4. Gypseous Marl. Gypseous with Bones. Upper gypseous Marl. 5. Sandstone and Sand without Shells. Upper Marine Sandstone. Millstone without Shells. 6. Freshwater Limestone, including Marls, and Millstone, with freshwater Shells. 7. Alluvial Soil, ancient and modern, including Pebbles, Pudding-stone, Black Earth (les marnes argilleuses noires), and Peat. |