The Geological Observer

Preface

. It has been well remarked by Humboldt* that to behold is not necessarily to observe, that is, to compare and combine. The history of Geology, like that of all sciences depending for their effective advance on experiment or correct observation, amply proves the truth of this statement. We are not required to look far back to be fully aware of the many brilliant hypotheses which have given way before the advance of correct research. It was not that these brilliant hypotheses were intended as substitutes for sound geological knowledge, based on correct data, or that those who formed them were not as capable as any who may in after-times succeed in still farther systematically embodying the accumulated data of such times, but merely that correct observations were not then sufficiently abundant, and that powerful, and, sometimes, im patient minds often supplied their place with conceptions more captivating than Well founded.

It is obvious that with a hundred well-established facts more can be accomplished than with ten, the deductions from which, however apparently correct, may even be fallacious as respects those derived from the consideration of the greater number. Let it not, never theless, be hastily concluded that the views which have passed * Kosmos. VI

PREFACE.

. away have not materially advanced geology, as those of a similar character have aided the progress of other sciences. Without them, though a few may have been impediments for the time, many a subject would have longer remained disregarded by its zealous investigator. Even the controversies which have from time to time appeared, many from differences of opinion arising the more readily as the subject was less perfectly understood, gave a certain impulse to progress which the commencement of many inquiries so often demands. The following work was undertaken in the hope that the experience of many years might assist, and, perhaps, abridge the labours of those who may be desirous of entering upon the study of geology, and especially in the field. Its object is, to afford a general view of the chief points of that science, such as existing observations would lead us to infer were established ; to show how the correctness of such observations may be tested ; and to sketch the directions in which they may apparently be extended.

Having been, to a certain extent, founded upon a little treatise, entitled " How to Observe in Geology," long since out of print, a somewhat similar name has been retained for the present volume. H. T. De la Beche. CONTENTS. I. rAGE Introduction xxi II. Decomposition of rocks . . . . . . . . 1 Formation of soils . . . . ... . . . 1 Decomposition of granitic rocks . . . . . .3 Decomposition of sandstones and limestones 7 Influence of organic remains and structure on decomposition . . 8 Decomposition of rocks containing oxides of iron . . . .11 III. Removal of the parts of rocks by water 13 Soluble substances .......... 13 Carbonate of lime — travertine . . . . . . . .13 Analyses of running water ........ 15 Composition and specific gravity of sea water . . . . .16 Silica in water . . . . . . . . . .17 Hot springs, geysers ......... 18 Springs on the outcrop of strata 19 Springs on faults .......... 21 Cause of land-slips .......... 25 Substances mechanically suspended in water ..... 28 Transport of detritus by rivers ....... 29 Deposit of detritus in valleys 36 Action of rivers on their beds ........ 38 Removal of lakes by river action ....... 44 Formation and discharge of lakes ....... 46 IV.

Lacustrine deposits ......... 49 V. Action of the sea on coasts •••••■.. 53 Difference of tidal and tideless seas ....... 55 Unequal abrasion of coasts . . . ..... 59 Shingle beaches .......... 63 Chesil Bank ........... 65 Coast sand-hills .......... CONTENTS. VIII vi. Distribution and deposit of sediment in tideless seas .... 72 Deposits of the Nile . - . . . . . . • .73 Of the Po and Rhone 75 Contemporaneous deposits of gravel, sand, and mud .... 77 Volcanic ashes and lapilli ........ 79 Deposits in the Black Sea and the Baltic ...... 83 Influence of ice in the Baltic ........ 85 Gulf of Mexico and Mississippi ....... 86 VII. Distribution and deposit of sediment in tidal seas ..... 88 Bars at river mouths . ' . . . . . . . .89 Rise and influence of the tides ........ 90 Deposits in estuaries ......... 96 Delta of the Ganges .... . . ... 98 Of the Quorra • . .99 Deposits on the coast near Swansea ....... 101 Influence of waves .......... 102 Form of the sea bed round the British Islands ..... 104 Influence of currents ......... 107 Specific gravity of sea water . . . . . . . .111 Distribution of sediment over the floor of the ocean . . . .113 VIII.

Chemical deposits in seas . . . . . . . . .117 Deposits in the Caspian and inland seas . . . . . .118 Calcareous deposits . . . . . . . . . .122 Formation of oolitic rocks. ........ 123 Salts in sea water .......... 124 IX. Preservation of remains of existing life in mineral matter . . . 128 Plants and vegetable matter . . . . . . . . 1 29 Bogs 130 Dismal Swamp ........ . 131 Rafts in the Mississippi . . . . . . . . .133 Animal remains—on the land ........ 135 Vertebrata . . . . . . . . . . .135 Ossiferous caverns and lake deposits ....... 136 Insects ............ 913 Land molluscs . . . . . . . . , .140 Effects of showers of volcanic ashes ....... 141 Estuary deposits . . . . . . . . . .145 Foot prints on mud .......... 147 Marine deposits and remains . . . , . . . .150 Modification of conditions on coasts of America . . . . .151 CONTENTS.

IX TAGE Ofthe Pacific Ocean 154 Of the Indian Ocean . . . . . . . . .157 Coasts of Africa and Europe .. . . . . . .159 Arctic Sea ........... 160 Distribution of marine life ........ 163 Modifications from temperature and pressure . . . • .164 From light and supply of air . . . . . . .166 Researches of Professor E. Forbes in the Ægean Sea .... 167 Zones of depth .......... 168 Professor Loven on the molluscs of Norway ■ • ■ • .173 Zones of depth in the British seas . . . . . • .175 Organic remains deposited in the deep ocean ..... 179 On coasts ........... 181 Coral reefs and islands . . . . ■ • • • .190 Distribution of coral animals . . . . • . • .190 Chemical composition of coral . . . . • . ■ .193 Keeling atoll 194 Form of coral islands ......... 199 Barrier reefs ........•■• 203 Lagoon Islands . . . • • ■ . • • • 204 Isle of Bourbon 206 Great barrier reef of Australia 208 Coral reefs of the Red Sea 21g Conditions for the occurrence of coral reefs . . . . .214 Influence of volcanic action on coral reefs . . . . . .219 Composition of coral reef accumulations ...... 222 Influence of changes in the level of sea and land ..... 225 Reefs near Bermuda ....••■■• 229 X. Transportal of mineral matter by ice 237 Height of snow line ....•■•••• 239 Glaciers 240 Cause of the movement of glaciers 245 Glacier moraines .......... 248 Motion of glaciers .....•■••• 251 Grooving of rocks by glaciers 254 Advance and retreat of glaciers ... . . . . . 256 Glaciers of the Himalaya 258 Arctic glaciers reaching the sea 259 Northern icebergs and their effects 264 Antarctic glaciers and ice barrier 266 Geological effects of Antarctic icebergs . . . ." .272 Glaciers of South Georgia 275 Glaciers of South America 276 Transportal of detritus by river ice 278 Geological effects of coast ice 282 Effects of grounded icebergs 285 General geological effects of ice X CONTENTS.

PAOF. Influence of a general increase of cold ...... 289 Modifications of temperature from changes in the distribution of sea and land 290 Erratic blocks 294 Effects of gradual rise of the sea-bottom strewed with ice-transported detritus 296 Effects of a supposed depression of the British Islands .... 299 Increase of Alpine glaciers ........ 304 Transportal of erratic blocks by glaciers ...... 308 Former existence of glaciers in Britain ...... 310 Elevation of boulders by coast ice during submergence of land . .312 Erratic blocks of the Alps 313 Erratic blocks of Northern Europe . . . . . . .319 Erratic blocks of America ........ 318 Mollusc remains in superficial detritus ...... 321 Arctic shells found iu British deposits ...... 323 Evidence of a colder climate in Britain .. . . . . . 324 Extinct Siberian elephant ......... 327 Changes of land and sea in Northern Europe ..... 331 Extinction of the great Northern mammals ..... .332 Range of the Mammoth ......... 333 Frozen soil of Siberia ......... 335 XI.

Ossiferous caves and osseous breccia ....... 336 Former connexion of Britain with the Continent . .... 337 Mammoth remains found in British seas ...... 333 Kirkdale Cave 342 Mud in ossiferous caves ......... 344 General state of these caverns ....... 345 Human remains in Paviland Cave ..... 347 Caves formed dens of extinct carnivora ...... 343 Human remains in ossiferous caverns ..... 350 Complicated accumulations in bone caves . . • . . . 352 Pebbles in ossiferous caves ..... 354 Deposits in subterranean river channels .... 35c Osseous breccia in fissures .... oe-a usseous ureccia 111 nssures ...... q--c Changes in the entrances to caves ..... ofii Occurrence of Mastodon remains .... 3g3 Association with those of the Mammoth .... 364 Extinct mammals of Central France . . . „„. 365 XII. Volcanos and their products ....

Height above the sea Craters of elevation and eruption Fossiliferous volcanic tuff beds .... Several craters on one fissure . CONTENTS.

XI PAGE Volcanic vapours and gases ........ 373 Volcanic sublimations ......... 375 Molten volcanic products ......... 376 Flow of lava streams ......... 377 Vesicular lavas .......... 379 Volcanic cones .......... 383 Cotopaxi ........... 384 Volcanos of Hawaii .......... 385 Effects of the lava on trees . . . . . . . .392 Vesuvius ........... 394 Etna 396 Iceland ............ 396 Stromboli in constant activity ........ 398 Intervals of long quiescence ........ 399 Sudden formation of Jorullo ........ 400 Sudden formation of Monte Nuovo ....... 401 Falling in of the volcano Papandayang in Java ..... 402 Subterranean lakes with fish ........ 403 Discharge of acid waters ......... 404 Inundations from volcanos ........ 405 Chemical nature of volcanic products ...... 406 Trachyte and dolerite ......... 407 Composition of the felspathic minerals ...... 410 Composition of lava rocks ........ 412 Composition of obsidians . . . . . . . . .413 Composition of olivine and leucite ....... 414 Diffusion of minerals in volcanic rocks ...... 416 Fusibility of minerals in volcanic rocks ...... 417 Sinking of minerals in fused lava . . . . . . .418 Fusion of rocks broken off in volcanic vents . . . . .419 Lamination of streams of lava ........ 420 Laminæ of spherules in obsidian ....... 421 Composition of volcanic ashes ........ 422 Modified composition of volcanic ashes ...... 423 Volcanic tuff ........... 424 Composition of palagonite tuff of Iceland ...... 425 Modification of volcanic tuffs by gases and vapours .... 426 Solution of palagonite tuff in acids ....... 428 Solfataras ........... 429 The Geysers, and their mode of action, Iceland ..... 430 Siliceous deposits from the Geysers ....... 432 Sulphurous waters of Iceland ........ 433 Gypsum deposits of Iceland ........ 434 Fusibility of volcanic products ........ 436 Fissures in volcanos filled by molten lava ...... 437 Lava ejected through fissures ........ 4.39 Direction of fissures in volcanos ....... 440 Effects of sea on volcanic gases . . . . . . . . 44 1 Softening and raising of tuffs and lavas ...... 442 The Caldera, Island of Palma CONTENTS.

PAGE Sections of Etna and Vesuvius ......•• 445 Form and structure of Etna ........ 446 Origin of the Val del Bove, Etna 447 Fossiliferous volcanic tuff of Monte Somma, Vesuvius .... 448 Mixed molten volcanic rocks and conglomerates ..... 449 Modification of submarine volcanic deposits ..... 450 Peak of Teneriffe 451 Santorin group .......... 452 Raised fossiliferous, volcanic tuff of Santorin group . . • 455 Quiet deposits inside the Santorin group ...... 457 Island of St. Paul, Indian Ocean . . . . . • .458 Distribution of volcanos in the ocean ....... 459 Distribution of volcanos on continents, and amid inland seas . . .461 Variable proximity of volcanos to water ...... 463 Extinct volcanos .......... 464 Mineral and chemical composition, and structure of basalt . . . 465 XIII. Salses or mud volcanos ......... 472 Nitrogen evolved from mud volcanos, Taman ..... 477 Boracic acid of Tuscany ......... 478 XIV.

Earthquakes ........... 479 Connexion of volcanos and earthquakes ...... 480 Extent of earthquakes ......... 482 Movement of the earth-wave during earthquakes 483 Sea-waves produced during earthquakes ...... 484 Transmission of earthquake-waves complicated by different mineral structures ........... 486 Unequal transmission of earthquakes ....... 488 Locally extended range of earthquakes ...... 489 4 Earthquakes traversing mountain chains ...... "490 Fissures produced during earthquakes ...... 491 Settlement of unconsolidated beds adjoining hard rocks during earthquakes 492 Breaking of great sea-wave, of earthquakes, on coasts .... 494 Effects of earthquakes on lakes and rivers ..... 495 Flame and vapours from earthquake fissures .... 496 Sounds accompanying earthquakes ...... 497 Elevation and depression of land during earthquakes .... 498 Coast of Chili raised during earthquakes .... 500 Effects of earthquakes in the Runn of Cutch 501 XV.

Quiet rise and subsidence of land ..... 502 Rise and depression of coast in the Bay of Naples . . 504 Elevation and depression of land from increase and decrease of heat CONTENTS. XIII PAGE Gradual rise of laud in Sweden and Norway ..... 508 Raised coasts in Scandinavia ........ 509 Gradual depression of land in Greenland ...... 510 Movements of coasts in the Mediterranean . . . . . .511 Unstable state of the earth's surface . 512 XVI. Sunk (submarine) forests and raised beaches . . . • .513 Sunk forests of Western Europe . . . . . . .514 Sunk forests beneath the sea in roadsteads ...... 515 Mode of occurrence of sunk forests . . . . . . .516 Localities of sunk forests . . . . • • . • .517 Remains of mammals and insects in sunk forests of Western England . 518 Foot-prints of deer and oxen amid the rooted trees of sunk forests in South Wales 520 Sunk forests viewed with regard to the varied heights of tide on tidal coasts ........... 522 Raised beaches concealed by detritus ...... 524 Raised beaches of Plymouth, Falmouth, and New Quay . . . 525 Raised dunes of blown sand, Perran Bay, Cornwall .... 529 Distribution of detritus in the English Channel, and in sea south of Ireland 5.0 Care required in tracing raised coast lines ...... 532 Raised coast lines, Scandinavia ....... . 533 XVII.

Temperature of the earth ......... 534 Temperature of different depths in Siberia ...... 535 Temperatures found in Artesian wells ...... 536 Heat of waters rising through faults, and other fissures . . . 537 Variable temperature from unequal percolation of water through rocks . 538 Temperature of waters in limestone districts ..... 542 XVIII. Mode of accumulation of detrital and fossiliferous rocks . . . 543 Detrital rocks chiefly old sea-bottoms ...... 544 Mixture of beds with and without fossils ...... 545 Variable mode of occurrence of organic remains among detrital and fossiliferous rocks .......... 546 Beaches on the shores of land at the time of the Silurian deposits and old red sandstones .......... 548 Beaches of the new red sandstone period in the Mendip Hills, and near Bristol 550 Beaches at the time of the lias 554 Lias resting on disturbed beds of carboniferous limestone . . . 556 Varied modes of occurrence of the lias ...... 558 Boring molluscs of the inferior oolite period CONTENTS.

PAGE Overlap of the inferior oolite, Mendip Hills ..... 560 Lias conglomerate, pierced by boring molluscs ..... 561 Land of the time of the lias 562 Evidence of land from fresh-water deposits ...... 563 Effects produced on coasts, rivers, and lakes, by continued elevation of land above sea .......... 564 Elevation of land over a wide area ....... 566 Effects of closing the Straits of Gibraltar 567 Unequal elevation of land ........ 568 Lakes on the outskirts of mountains ....... 569 Mixture of organic remains of different periods from submergence of laud . 572 Variable effects of submergence of present dry land .... 574 Evidence afforded by the coal-measures ...... 576 Stigmaria beds in the coal-measures ...... 577 Stems of plants in their positions of growth in the coal-measures . . 578 Filling up of hollow vertical stems, and mixture of prostrate plants with them 580 Growth of terrestrial plants in successive planes in the coal-measures . 582 Thickness of South Wales coal-measures ...... 584 False bedding in coal-measure sandstones ...... 585 Surfaces of coal-measure sandstones ....... 586 Drifts of matted plants in the coal-measures ..... 587 Extent of coal-beds 588 Partial removal of coal-beds ........ 589 Channels eroded in coal-beds, Forest of Dean ..... 590 Lapse of time during deposit of coal-measures ..... 591 Pebbles of coal in coal accumulations ...... 592 Marine remains in part of the coal-measures ..... 593 Gradual subsidence of delta lands ....... 594 Fossil trees and ancient soils, Isle of Portland ..... 595 Conditions under which the ancient soils and growth of plants were pro duced at Portland ......... 596 Wealden deposits, South-eastern England ...... 598 Raised sea-bottom round British Islands ...... 599 Overlap of cretaceous beds in England ..... 600 Cracked surfaces of deposits . . . . . . . .601 Foot-prints of air-breathing animals on surfaces of rocks . . . 603 Rain-marks on surfaces of rocks ....... 604 Elevation or depression of the bottom in the ocean .... 605 Character of the surfaces of rocks ....... 606 Friction-marks on rock surfaces ....... 6Q7 Ridged and furrowed surfaces of rocks ...... 609 Effects of earthquakes on sea-bottoms . . . . . .fill Diagonal arrangement of the minor parts of beds among detrital rocks . 612 Beds formed by unequal drifts . . . . . . . .614 Mode of occurrence of organic remains ...... 615 Distribution of organic remains . . . . . . .621 Effect ofthe rise and fall of land on the distribution of organic remains . 626 Distribution of organic remains with respect to different kinds of sea-bottoms •••••......

CONTENTS. XV PAiPE Infusorial remains .......... 630 Chemical composition of organic remains ...... 631 Caution as to forms of life supposed characteristic of different geological times ............ 632 XIX. Igneous products of earlier date than those of modern volcanos . . 633 Simple substances forming igneous rocks ...... 634 Volcanic products amid the older rocks ...... 635 Fossils amid old igneous products ....... 637 Volcanic tuff and conglomerates among the Silurian deposits of Wales and Ireland 638 Old volcanic products intermingled with the Devonian rocks of South-western England .......... 640 Igneous rocks associated with the carboniferous limestone of Derbyshire . 642 Relative geological date of the Wicklow and Wexford granites . . . 646 Date of the granites of Devon and Cornwall . . . . 648 Uncertain dates of some igneous dykes ...... 649 Granitic or porphyry dykes, known as elvans in Cornwall and Devon . 650 Igneous rocks in the lower portion of the new red sandstone series in Devonshire ........... 652 Dates of the Cornish and Devonian elvans ...... 654 Elvans of Wicklow and Wexford ....... 655 Chemical composition of igneous rocks ...... 656 Effect of silicate of lime in igneous rocks ...... 657 Mode of occurrence of granites in South-western England aud South-eastern Ireland .......... 658 Outline of the granite range of Wicklow ...... 660 Granite veins 661 Chemical composition of granitic rocks ...... 663 Schorlaceous granites of Cornwall and Devon .....

CC4 Slight covering of granite by the older rocks in Wicklow, Wexford, and Cornwall 666 Serpentine and diallage rock of Cornwall 668 Serpentine of Caernarvonshire ........ 669 Serpentine of Anglesea ......... 67o Chemical composition of serpentine . . . . . . .671 Composition of serpentine and olivine compared .... 672 Composition of greenstone and syenite ...... 673 Resemblances and differences between the ordinary granitic and hornblendic rocks .......... 674 Granitic, felspathic, hornblendic, and serpentinous rocks ejected at various times 676 Relative fusibility of igneous rocks 678 Modification of the matter of igneous rocks 679 Additional minerals entering into the composition of ordinary igneous rocks .... 680 General character of igneous rocks CONTENTS.

XX- PAGE Consolidation and adjustment of the component parts of rocks . . 683 Adjustment ofthe component parts of calcareous and argillaceous deposits 684 Arrangement of similar matter in nodules ...-•• 686 Central fractures in septaria ........ 687 Nodules of phosphate of lime in rocks ...... 688 Spheroidal concretions in the Silurian rocks ..... 689 Crystals of iron pyrites in clays and shales . ..... 690 Mode of occurrence of sulphate of lime . . • • • .691 Modification in the structure of rocks from exposure to changes of temperature ........... 692 Chloride of sodium disseminated amid rocks ..... 694 Variable deposits of detrital matter ....... 695 Importance of silica and the silicates in the consolidation of the detrital rocks ............ 696 Alteration of rocks, on minor scale, by heat ..... 698 Formation of crystals in altered rocks ..... 699 Crystalline modification of rocks ....... 700 Alteration of rocks near granitic masses ...... 701 Readjustment of parts of igneous rocks ...... 702 Production of certain minerals in altered rocks ..... 703 Mineral matter transmitted into altered rocks ..... 704 Mica slate and gneiss ......... 705 Cleavage of rocks .......... 706 Cleavage in sandstones and shales ....... 707 Cleavage in shales and limestones ....... 708 Minor interruptions to cleavage action ...... 709 Cleavage on the large scale ........ 710 Range of cleavage through contorted rocks . . . . . .711 Double cleavage ....... ... 712 Relative dates of cleavage . . . . . . . .713 Elongation and distortion of organic remains by cleavage action . . 714 Different directions of cleavage in the same or juxtaposed districts . 716 Joints in rocks . . . . . . . . . .718 Directions and range of joints . . . . . . . .719 Joints in granite .......... 720 Joints in sedimentary rocks . . . . . . . .721 Joints among conglomerates ........ 722 Joints in limestone .......... 723 Movement of rocks after jointing ....... 724 Complication of bedding, jointing, and cleavage ..... 725 XXI.

Bending, contortion, and fracture of bedded rocks .... 726 Earth's radius compared with mountain heights ..... 727 The volume of the earth compared with mountain ranges . . . 728 Effects of a gradually cooling globe ....... 730 Mountain ranges viewed on the large scale . . . . . .731 CONTENTS. XVII paos Directions of mountain chains ........ 732 Conditions effecting the obliteration or preservation of mountain chains . 734 Lateral pressure of beds of rock amid mountains . .... 736 Bending and folding of deposits in the Appalachian zone, North America 739 Flexures and plications of rocks in the Alps, and district of older deposits of the Rhine 740 Igneous rocks amid contorted beds . . . • • • .742 Contorted coal-measures of South Wales ...... 743 Contortion of the component parts of beds ...••• 744 Faults 745 Production and direction of fissures through rocks . 746 Evidence of the relative dates of fissures ..••■• 749 Fallacious appearance from a single movement shifting various fissures . 752 Fissures split at their ends ....■••■ "54 Lines of least resistance to fissures ..-•••• 755 Range of mineral veins and common faults in South Western England . 757 Range of faults near Swansea ....-••• 759 Inclination of faults . . . . ■ • ■ • . /60 Parts of deposits preserved by feults . - • • • • .761 Complicated faults "62 XXII.

Filling of fissures and other cavities with mineral matter . . .763 Sulphurets of lead, copper, &e., replacing shells 764 Filling of minor fissures ....••••■ "65 Solubility and deposit of mineral matter in fissures .... 766 Solubility of sulphate of baryta 768 Deposits from solutions in fissures ....••■ 769 Effects produced in heated fissures beneath seas 770 Many similar substances found in mineral springs and veins . . .771 Frequent occurrence of sulphur, arsenic, &c, with certain metals in mineral 779 veins . . . ■ • • • • • • ' ' '" Action and re-action of substances upon each other in fissures and cavities 774 Character of metalliferous veins amid associated dissimilar rocks . . 776 Condition of mineral veins traversing elvan dykes in Cornwall . .778 Influence of the different rocks traversed on the mineral contents of fissures ....••••••• 780 Mode of occurrence of lead ores amid the limestones and igneous rocks of Derbyshire ....••■•••■ '°-* 4 Flats ' of lead ore in limestone districts 784 Metalliferous deposits in the joints of rocks 786 Relative different dates of mineral veins 789 Modification of the contents of mineral veins in their depth and range . 790 Modifications of the upper part of mineral veins from atmospheric in- 799 fluences .'.','. nuences ._.•■--- Sulphurets of lead and zinc converted into carbonates in mineral veins . 794 Replacement of mineral matter of one kind by another in veins . . 796 Coating of the -walls of fissures by layers of mineral matter . • .798 Fissures coated by dissimilar substances . . • ■ -800 798 b CONTENTS. ri.pp Several successive movements through the same fissure . . • 801 Sliding of the sides of fissures on mineral matter accumulated in them at intervals ........... 804 Fractures through the mineral contents of fissures .... 806 Modification of the contents of fissures at the crossing of veins . • 807 Effects ou the contents of fissures meeting or crossing at small angles . 808 XXIII. * Partial removal or denudation of rocks ...... 809 Great denudation arising from the action of breakers . . . .810 Ancient exposure of the coasts of the area of the British Islands to the Atlantic 811 Care required respecting the amount of denudation of overlapping rocks . 812 Island masses of deposits left by denudation . . . . .813 Districts of bent and plicated beds worn down by denudation . . 814 New slices of land now being cut away by breaker action . . . 816 Amount of matter removed by denudation . . . . . .817 Denudation in parts of England and Wales ..... 818 Needful attention to the greater geological problems .... 820 XXIV.

Appendix : — Geological maps and sections ....... 821 Additional notices of subjects mentioned previously . . . CORRECTIONS. Page 4, line 26, for Bousdorf read Bonsdorf. — 14 — .36 ,, If this kind ,, Of this kind. — 83 — 14 ,, over the saline waters ,, over its saline waters. — 123 — 22 ,, the accumulations ,, these accumulations. — 125 — 35 , , Schweiger , , Schweitzer. — 156 — 36 , , effecting animal life ,, affecting animal life. — 171 — 15 ,, to illustrate the bands ,, to be illustrated by the bauds. — 211 — 18 ,, the land. Between ,, the land, between. — 213 — 21 , , clumps or branching ,, clumps of branching. — 259 — 17 , , they now are , , it now is. — 263 — 7 , , M. Ch. Martius , , M. Ch. Martins. — 327 — 20 ,, in 1822 ,, in 1802. — 332 — 27 , , Keyserbeg , , Keyserling. — 337 — 19 ,, Selkirk ,, Falkirk. — 347 — 31 , , latideus , , latidens. — 365 — 18 ,, angustideus ,, angustidens. — 375 — 22 , , silenium , , selenium. — 383 — 21 ,, Catopaxi ,, Cotopaxi. — 419 — 32 ,, Pentallaria ,, Pantellaria. — 467 — 7 ,, and partial ,, or partial. — 513 — 20 , , is here ,, are here. — 527 — • 14 , , covered at 4 , , covered at d. — 547 — 8 , , was found , , was formed. — 572 — 20 , , have not succeeded , , have succeeded. — 592 — 2 , , pebbles of it , , pebbles of them. b2 INTKODUCTION.

Observations have now been sufficiently extended and multiplied to show that, during a long lapse of time, the surface of our planet has been undergoing modifications and changes. Of these the most marked have been produced by the uprise of mineral matter in a molten state from beneath that surface ; the wearing away and removal to other localities of this matter, either in its first state, after cooling, or in some secondary con dition, by atmospheric influences and waters variously distributed for the time being; the preservation ofthe remains of animal and vegetable life during at least a portion of this lapse of time amid deposits accumulated, for the most part, in horizontal layers beneath waters, and by the unquiet state of the earth's surface itself, from which, while considerable areas have been at different times raised slowly above, and depressed beneath the level of the ocean, occasionally whole masses of mineral matter of various kinds have been squeezed, bent, and plicated, sometimes ridged up into ranges of mountains.