| PERMIAN | 19. PERMIAN. | British Upper Permian of St. Bees’ Head, Cumberland ([p. 386]). Middle Permian, magnesian limestone, and marl-slate of Durham andYorkshire, with Protosaurus ([p. 387]). Lower Permian sandstones and breccias of Penrith andDumfriesshire, intercalated ([p.390]). Foreign Dark-coloured shales of Thuringia ([p. 392]). Zechstein or Dolomitic limestone ([p.392]). Mergel-schiefer or Kupfer-schiefer ([p. 392]). Rothliegendes of Thuringia, with Psaronius ([p. 392]). Magnesian limestones, etc., of Russia ([p. 393]). |
| CARBONIFEROUS | 20. UPPER CARBONIFEROUS. | British Coal-measures of South Wales, with underclays inclosingStigmaria ([p. 397]). Coal-measures of north and central England ([p. 395]). Millstone grit ([p. 395]). Yoredale series of Yorkshire ([p.395]). Coal-field of Kilkenny with Labyrinthodont ([p. 407]). Foreign Coal-field of Saarbruck, with Archegosaurus ([p. 406]). Carboniferous strata of South Joggins, Nova Scotia ([p. 409]). Pennsylvania coal-field ([p.403]). |
| 21. LOWER CARBONIFEROUS. | British Mountain limestone of Wales and South of England ([p. 430]). Same in Ireland ([p. 437]437). Carboniferous limestone of Scotland alternating with coal-bearingsandstones ([p. 396]). Erect trees in volcanic ash in the Island of Arran ([p. 546]). Foreign Mountain limestone of Belgium ([p.436]). | |
| DEVONIAN or OLD REDSANDSTONE | 22. UPPER DEVONIAN. | British Yellow sandstone of Dura Den, with Holoptychius, etc. ([p. 440]); and of Ireland withAnodon Jukesii ([p.441]). Sandstones of Forfarshire and Perthshire, withHoloptychius, etc. ([p.442]). Pilton group of North Devon ([p.449]). Petherwyn group of Cornwall, with Clymenia andCypridina ([p. 451]). Foreign Clymenien-kalk and Cypridinen-schiefer of Germany ([p. 450]) |
| 23. MIDDLE DEVONIAN. | British Bituminous schists of Gamrie, Caithness, etc., with numerous fish([p. 443]). Ilfracombe beds with peculiar trilobites and corals ([p. 450]). Limestones of Torquay, with broad-winged Spirifers ([p. 451]). Foreign Eifel limestone, with underlying schists containingCalceola ([p. 453]). Devonian strata of Russia ([p.454]). | |
| 24. LOWER DEVONIAN. | British Arbroath paving-stones, with Cephalaspis andPterygotus ([p. 446]). Lower sandstones of Forfarshire, with Pterygotus ([p. 446]). Sandstones and slates of the Foreland and Linton ([p. 454]). Foreign Oriskany sandstone of Western Canada and New York ([p. 456]). Sandstones of Gaspe, with Cephalaspis ([p. 455] ). |
| SILURIAN | 25. UPPER SILURIAN | British Upper Ludlow formation, Downton sandstone, with bone-bed ([p. 459]). Lower Ludlow formation, with oldest known fish remains ([p. 461]). Wenlock limestone and shale ([p.465]). Woolhope limestone and grit ([p.467]). Tarannon shales ([p. 468]). Beds of passage between Upper and Lower Silurian: Upper Llandovery, or May-hill sandstone, with Pentamerusoblongus, etc. ([p. 468]). Lower Llandovery slates ([p.469]). Foreign Niagara limestone, with Calymene, Homalonotus, etc. ([p. 479]). Clinton group of America, with Pentamerus oblongus, etc.([p. 479]). Silurian strata of Russia, with Pentamerus ([p. 477]). |
| 26. LOWER SILURIAN. | British Bala and Caradoc beds ([p.470]). Llandeilo flags ([p. 473]). Arenig or Stiper-stones group (Lower Llandeilo of Murchison) ([p. 475]). Foreign Ungulite or Obolus grit of Russia ([p. 477]). Trenton limestone, and other Lower Silurian groups of NorthAmerica ([p. 479]). Lower Silurian of Sweden ([p.477]). | |
| CAMBRIAN | 27. UPPER CAMBRIAN. | British Tremadoc slates ([p. 483]). Lingula flags, with Lingula Davisii ([p. 484]). Foreign “Primordial” zone of Bohemia in part, with trilobites of thegenera Paradoxides, etc. ([p.487]). Alum schists of Sweden and Norway ([p. 489]). Potsdam sandstone, with Dikelocephalus and Obolella([p. 489]). |
| 28. LOWER CAMBRIAN. | British Menevian beds of Wales, with Paradoxides Davidis, etc. ([p. 484]). Longmynd group, comprising the Harlech grits and Llanberis slates([p. 485]). Foreign Lower portion of Barrande’s “Primordial” zone in Bohemia([p. 486]). Fucoid sandstones of Sweden ([p.489]). Huronian series of Canada? ([p.490]). | |
| LAURENTIAN | 29. UPPER LAURENTIAN. | British Fundamental gneiss of the Hebrides? ([p. 493]). Hypersthene rocks of Skye? ([p.491]). Foreign Labradorite series north of the river St. Lawrence in Canada ([p. 491]). Adirondack mountains of New York ([p.491]). |
| 30. LOWER LAURENTIAN. | British Wanting? Foreign Beds of gneiss and quartzite, with interstratified limestones, inone of which, 1000 feet thick, occurs a foraminifer, EozoonCanadense, the oldest known fossil ([p. 491]). |
CHAPTER IX.
CLASSIFICATION OF TERTIARY FORMATIONS.
Order of Succession of Sedimentary Formations. — Frequent Unconformability of Strata. — Imperfection of the Record. — Defectiveness of the Monuments greater in Proportion to their Antiquity. — Reasons for studying the newer Groups first. — Nomenclature of Formations. — Detached Tertiary Formations scattered over Europe. — Value of the Shell-bearing Mollusca in Classification. — Classification of Tertiary Strata. — Eocene, Miocene, and Pliocene Terms explained.
By reference to the tables given at the end of the last chapter the reader will see that when the fossiliferous rocks are arranged chronologically, we have first to consider the Post-tertiary and then the Tertiary or Cainozoic formations, and afterwards to pass on to those of older date.
Order of Superposition.—The diagram (Fig. 86) will show the order of superposition of these deposits, assuming them all to be visible in one continuous section. In nature, as before hinted [(p. 107)], we have never an opportunity of seeing the whole of them so displayed in a single region; first, because sedimentary deposition is confined, during any one geological period, to limited areas; and secondly, because strata, after they have been formed, are liable to be utterly annihilated over wide areas by denudation. But wherever certain members of the series are present, they overlie one another in the order indicated in the diagram, though not always in the exact manner there represented, because some of them repose occasionally in unconformable stratification on others. This mode of superposition has been already explained [(p. 94,] [p. 111]), where I pointed out that the discordance which implies a considerable lapse of time between two formations in juxtaposition is almost invariably accompanied by a great dissimilarity in the species of organic remains.
Frequent Unconformability of Strata.—Where the widest gaps appear in the sequence of the fossil forms, as between the Permian and Triassic rocks, or between the Cretaceous and Eocene, examples of such unconformability are very frequent. But they are also met with in some part or other of the world at the junction of almost all the other principal formations, and sometimes the subordinate divisions of any one of the leading groups may be found lying unconformably on another subordinate member of the same—the Upper, for example, on the Lower Silurian, or the superior division of the Old Red Sandstone on a lower member of the same, and so forth. Instances of such irregularities in the mode of succession of the strata are the more intelligible the more we extend our survey of the fossiliferous formations, for we are continually bringing to light deposits of intermediate date, which have to be intercalated between those previously known, and which reveal to us a long series of events, of which antecedently to such discoveries we had no knowledge.
But while unconformability invariably bears testimony to a lapse of unrepresented time, the conformability of two sets of strata in contact by no means implies that the newer formation immediately succeeded the older one. It simply implies that the ancient rocks were subjected to no movements of such a nature as to tilt, bend, or break them before the more modern formation was superimposed. It does not show that the earth’s crust was motionless in the region in question, for there may have been a gradual sinking or rising, extending uniformly over a large surface, and yet, during such movement, the stratified rocks may have retained their original horizontality of position. There may have been a conversion of a wide area from sea into land and from land into sea, and during these changes of level some strata may have been slowly removed by aqueous action, and after this new strata may be superimposed, differing perhaps in date by thousands of years or centuries, and yet resting conformably on the older set. There may even be a blending of the materials constituting the older deposit with those of the newer, so as to give rise to a passage in the mineral character of the one rock into the other as if there had been no break or interruption in the depositing process.