Lyellʼs folding map Plate 1 to illustrate that the position of land and sea is not fixed. The hand lens for scale has outside frame diameter 2.5 cm (1 inch). From Lyell (1837)

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... -Let us now turn from the contemplation of the winter of the "great year," and consider the opposite train of circumstances which would bring on the spring and summer. To imagine all the lands to be collected together in equatorial latitudes, and a few promontories only to project beyond the thirtieth parallel, as represented in the annexed map ( Fig. 1. Pl. I.), would be undoubtedly to suppose an extreme result of geological change. But if we consider a mere approximation to such a state of things, it would be sufficient to cause a general elevation of temperature. Nor can it be regarded as a visionary idea, that, amidst the revolutions of the earth's surface, the quantity of land ...

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... the "theory of submergence"; that tropical plants had grown in England and then been submerged and turned into coal. He wrote, in italics, "It is assumed that there was a period in the history of our globe when a damp and steamy heat ... prevailed on the surface of the earth." He showed a figure depicting this type of tropical fern-tree forest (Fig. 10), and another figure showing some of the plant fossils that were the basis of these geological interpretations. We now continue Pepperʼs presentation, although to reduce its length, I have cut off most of his seven detailed arguments here after the first few words. Then comes the part of Pepperʼs text where he presented Hopkinsʼ ...

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... 1 Hopkins had not illustrated these stratigraphic units, but Pepper did. Therefore, I show some of Pepperʼs illustrations of these layers as they occur in England (Figs. 11 and 12). The Mountain Limestone, just below the coal strata, also had fossils that indicated warm tropical seas. Pepper illustrated these fossils as well ( Fig. 13): Figure 13. Fossils from a warm shallow sea at the time of the coal deposits. From Pepper ...

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... than 25 years, and distributed from London, New York, and Australia by the publisher Routledge. The early printings were dated: 1861, 1862, 1866, and 1869. After that, no dates were shown. Some of the later printings were claimed to be "A New Edition" although all the printings were exactly the same. The volume was given many different covers (Fig. 14). Copies were often bound in full leather, embossed with a schoolʼs emblem, and awarded at graduation ceremonies to the student who had most excelled in science during the year. Pepper's Playbook of Metals (later called the Boy's Book of Metals) was bound in brightly decorated covers and spines during the decades that it was in ...

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... geologist Jules Marcou (1824-1898) worked with the same ideas, and in 1860 he became the first scientist to publish a map showing a continent spanning the Atlantic Ocean. In his Carte du Globe a lʼépoque jurassique he showed the continents of America, Africa and Australia to be connected as the single land mass "Américo-Africo-Australie" (Fig. 15). He based his interpretations on Jurassic marine fossils. These fossils were much younger, and urelated to the land-fossils that Lyell and Hull had used as evidence for a similar continental connection. Note the great width of Marcouʼs connection. North America and Africa were united by a landmass, not a mere chain of islands. Marcou ...

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... German paleontologist Melchior Neumayr (1845-1890) included many of these ideas in his 2-volume history of the Earth (Neumayr 1887). His Brazilian-Ethiopian Continent connected South America and Africa (Fig. 16). His Indo-Madagasic Peninsula, a similar land bridge that spanned the Indian Ocean, was already known by the name Lemuria (Sclater 1864). Lemurs are found on Madagascar but not in Africa, whereas fossils showed that lemurs had lived in India. It was presumed that the lemurs used the ancient Lemurian land bridge to get across the Indian ...

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... was presumed that the lemurs used the ancient Lemurian land bridge to get across the Indian Ocean. Figure 16. Neumayrʼs illustration of the southern continent in his textbook Erdgeschichte (Earth History). ...

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... does North America stand alone in the ocean, but the locations of the Precambrian rocks and the Cambrian sediments deposited on them convinced Dana that North America had stood alone since earliest time. He presented a map of the Precambrian rocks, which seems to show that the shape of the ancient continent matches the shape of the modern one (Fig. 17). Beginning with its solitary placement, it had developed mountain belts along its margins. The higher mountains faced the wider Pacific Ocean and the lower mountains faced the narrower Atlantic Ocean. These features, and others, seemed to make North America an ideal continent. Dana could explain in great detail how rocks, plants, ...

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... Fig. 17.], represents the main portion of the dry land of North America in the later part or at the close of the Azoic age; for it consists of the rocks made during the age, and is bordered, on its different sides, by the earliest rocks of the next age. It is, therefore, the beginning of the dry land of North America, the original nucleus of the ...

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... were not reading these books, and they were learning that North America had earlier been connected to the eastern continents. Figure 18. Five editions of Danaʼs Manual of Geology for colleges, five editions of his Text-book of Geology for schools, and The Geological Story, widely read by the general public. ...

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... Willis was North Americaʼs other pioneer paleogeographer. He was one of the leading geologists at the U. S. Geological Survey. He had compiled the wall-sized Geologic Map of North America and the 900-page Index to the Stratigraphy of North America. In 1910, he published a series of 15 paleogeographic maps of North America (Fig. 21) very much like Schuchertʼs. also wrote a 20-page article in the journal Science, entitled Principles of Paleogeography. It did not provide detailed map data and interpretations as Schuchert had done. Willisʼs purpose was more to lay out the fundamental principles of the new science of ...

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... joined together; dinosaurs and other reptiles were wandering freely across all the land areas: Schuchert 1915, p. 827-828. ...almost all of the twenty-five orders of Mesozoic reptiles were already represented in the Triassic, though often by comparatively small and rare forms. Their footprints are known in eastern North America in great variety (Figs. 460, 461), but good skeletons are exceedingly rare. In Europe, on the other hand, their skeletons are more common, and, so far as known, the animals were of the same kinds as those of America. From this and other evidence it appears that the great northern continent Eria (Fig. 434) was still intact and was the land across which the plants and ...

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... dinosaurs, however, were the lords of the land, and they were present in great variety and in great size; in fact, some known by their footprints only, must have been larger than elephants (Fig. 461). In the Upper Triassic they had become adapted to all the land habitats. ...

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... completely in construction and geologic history. Here, with fixed continents, one would have to suppose that these stubs were connected in the east and west by a chain 6700-km in length, which has sunk! With reconstructive joining of the South American and African masses, on the other hand, both portions are brought just into contact (cf. Fig. 17 on the next ...

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... his second edition in 1920, Wegener illustrated the whole supercontinent ( Fig. 31), not just the part that borders the present Atlantic Ocean. His second book was again in German, and not readily available to Englishspeaking geologists. A book review in English was written for Geological Magazine by Philip Lake . He was well known for his textbook on the geology of Great Britain ( Lake and Rastall, 1910.) From this ...

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... that in his Figure 1, Wegener chose Africa as the frame of reference, keeping it in the center of his displacement maps. He moved the other continents around, but not Africa. ...

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... the purpose he made use of the papers or maps of Arldt, Burckhardt, Diener, Frech, Fritz, Handlirsch, Haug, Ihering, Karpinsky, Koken, Koszmat, Katzer, Lapparent, Matthew, Neumayr, Ortmann, Osborn, Schuchert, Uhlig and Willis. The table of p. 74 shows an extract from Arldt's statistics, and the first four land-bridges are illustrated by curves in Fig. 15 [Fig. 34]. In this, three curves are drawn for each land-bridge, namely, for the number of votes in favour, of those in opposition, and of the difference, the latter thus giving the strength of the majority; this is emphasized by shading on the area concerned. These four early land-bridges are those extending over presentday oceanic areas, and ...

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... land was in the north and especially northeast, rising here to about 4000 feet above sea-level. The Transvaal ice sheet was the most extensive, moving at least 700 miles to the southwest. The tillites of the Dwyka series are in the northeast less than 100 feet thick, but in the south attain to 1500 feet, and in southern Karoo to 2000 feet (see Fig. 144, p. 428) [Fig. ...

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... was there stated that folding, thrusting, and up-ending of strata are the necessary results of pressure, exerted at the ends of the originally flat beds; that is, horizontal pressure. We recall Figures 142 and 143, giving sections which illustrate the experimental imitation of mountain folds and thrusts by lateral pressure; and we remember that mountain ranges are chiefly made of geosynclinal prisms, that is, very extensive and thick lenses of sedimentary, stratified rocks. ...

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... and Wegener believe that the mountain chains of the globe were formed by the horizontal crushing of geosynclinal prisms which lay in front of slowly moving, migrating continents. For example, according to this hypothesis, the formation of our Rocky Mountain system was due to the slipping of all North America in a westerly direction, away from Europe, and that for a distance of hundreds of miles ( Figure 163). This migration of the vast continental block took place under the direction of a force so powerful that the strata of the Rocky Mountain geosyncline were crumpled and thrust into mountain turmoil. ...

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... reproduced Wegenerʼs three globe maps as his Figure 163, and made very favorable comments. In a later section, Daly referred again to Wegenerʼs three maps, and followed them up with maps of his own, of the Atlantic (see Fig. 45) and the Pacific coastlines: ...

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... has attempted to reconstruct the original continent. The uppermost drawing of Figure 163, page 261, illustrates his conception of what the lands were like in the so-called Carboniferous period of the earth's history. The Americas are shown cheek by jowl with the Old World. ...

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... brief, the Atlantic and Pacific types of coast-line, fundamental features of the earth, are adequately explained by the hypothesis of the migration of continents. Figure 169 [ Fig. 45] is a map of the Atlantic basin with its great gulflike extension, the Arctic basin. The Circum-Pacific mountains of America are shown in solid black and are marked with the letter P. The east-west, older Hercynian-Appalachian system of the northern hemisphere is in part shown at I by axial lines. ...

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... zone where the New and Old Worlds were torn apart is plausibly regarded as the so-called Mid-Atlantic Swell, which is a long and broad "ridge" on the ocean's floor; its height averages about one mile, or 1,600 meters. The map of Figure 169 bears contour lines of the Atlantic bottom, at 500-meter intervals, from the 4,000-meter contour upward. These lines locate the Mid-Atlantic Swell. ...

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... a working hypothesis. He had read the book by Köppen and Wegener, with its valuable map-data on ancient climates and that showed paleoclimate zones. That book was not available in English, so Van der Gracht reproduced the ten essential world maps in his own 75-page paper. He even had English figure-texts and legends prepared for them (see their Fig. 1, p. 107.) Those ten figures were not in any way related to Van der Grachtʼs text; he simply distributed them evenly throughout it. His addition of these extraneous figures is the first clue that there were no strict limitations on the number of pages or illustrations in this symposium ...

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... paper showed convection currents much like those assumed today to operate in plate tectonics (Fig. 51). It included this ...

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... on reaching the top the material promotes subcrustal fusion and spreads out laterally, flowing horizontally to the neighboring descending currents. The horizontal flow is likely to exercise a powerful viscous drag on the lower levels of the crust, throwing the latter into tension where the currents diverge and into compression where they converge (Figs. 12 and 13.) If the distance between ascending and descending currents be of continental dimensions then the drag due to horizontal flow may produce continental displacements, with distension behind and mountain-building in front. Material from the substratum ascends into the distended area, where it cools and differentiates, while heavy ...

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... thick layer of folded and faulted rocks. It is bounded by thrust planes of great horizontal extent, both above and below. It may be identified by the age, stratigraphic sequence, and fossils of the strata composing it. Thus identified, the Alpine decken have been numbered and named, for instance, in Fig. 90. [see instead Fig. 56, which is Willisʼ Fig. ...

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... -During the Permian and the following Triassic, deserts were probably more widespread than at any other time save the present. The dune sands (Fig. 166), the red beds, and the widespread deposits of salt and gypsum in the central and western United States indicate a vast interior more arid than the present Great Basin. The salt beds that stretch from Kansas to New Mexico have been estimated to include 30,000 billion tons of salt and would require the evaporation of more than 22,000 ...

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... in 1941. Again the book was greatly revised, except for the paragraphs about the Permian paleogeography. The most significant change in that chapter was the removal of the 1923-map. How to replace this map must have been a problem, but Schuchert and Dunbar solved it in a very creative way. They found a base map that showed no Atlantic Ocean (Fig. 61). They could now remove the land bridges across the Atlantic, without the removal being obvious to those who knew the earlier editions. And on this new base map, the glacial deposits could be redrawn, and the arrows removed from South Africa. The Equator was broken and curved, so it was not easily noticed how close the glacial deposits ...

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... especially in the highly fractured region between Greenland and Canada, the map of which looks like a jig-saw puzzle with the separate bits dragged apart. In the Southern Hemisphere the originally continuous Gondwanaland similarly spread out, breaking up into immense rafts which also migrated towards the Equator and raised up mountains in front (Fig. 210). The basis of the South Atlantic and Indian oceans are interpreted as the stretched and broken regions left behind or between these drifting ...

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... and Triassic orogenic belts in South America which can be matched in South Africa. Here again, the crossing foreshadowed near the River Plate is accomplished behind Cape Town (Plate 95A). The distinguished South African geologist, Du Toit, has suggested that the Cape Folds are part of the same orogenic belt as that of eastern Australia (Fig. 261.) For many years Du Toit has been indefatigable in assembling the evidence bearing on continental drift. In his well-known book Our Wandering Continents he shows that a striking series of correspondences can be recognized in the sediments, fossils, climates, earth movements, and igneous intrusions of the two sides of the Atlantic. Both ...

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... were grouped together around the South Pole. In attempting a circumpolar reassembly the position to be allotted to Antarctica is necessarily uncertain. Wegener places it between Australia and South America (Fig. 260); whereas Du Toit, guided by meagre stratigraphical and tectonic clues, thinks it may have been between Australia and Africa ( Fig. 261) [Fig. 70]. With either arrangement the ice sheets all fall within an area comparable with that glaciated in the Northern Hemisphere during the Pleistocene. Moreover, as indicated in Fig. 260, the lateritic belt then comes into line with the Equator of the time, and other known details of the Carboniferous climatic girdles also fall ...

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... has been shown that in looking for a possible means of "engineering" continental drift we must confine ourselves to processes operating within the earth. To be appropriate, the process must be capable (a) of disrupting the ancestral Gondwanaland into gigantic fragments, and of carrying the latter radially outwards as indicated in Fig. 210: Africa and India toward the Tethys; Australasia, Antarctica, and South America out into the Pacific; (b) of disrupting Laurasia, though much less drastically, and again with radially outward movements towards the Tethys and the Pacific, as indicated in Fig. 209. We have already seen that the peripheral orogenic belts probably mark the ...

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... systems of sub-crustal currents came together and turned downwards. The movements required to account for the mountain structures are in the same directions as those required for continental drift, and it thus appears that the sub-crustal convection currents discussed on pages 408 to 413 may provide the sort of mechanism for which we are looking (Fig. 262) [Fig. ...

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... there can be nowhere else for them to go (Fig. 262). Now this is precisely what would be most likely to happen when two opposing currents come together and turn downwards beneath a cover of basaltic composition. The latter then suffers intense compression, and like the sial in similar circumstances it is eventually drawn in to form roots (c.f. Figs. 215 and 216). On the ocean floor the expression of such a down-turning of the basaltic layer would be an oceanic deep. The great deeps bordering the island festoons of Asia and the Australian arc (Tonga and Kermadec) probably represent the case where the sialic edge of a continent has turned down to form the inner flanks of a root, while the ...

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... districts belong to the Atlantic type, those of northwest Scotland belong to the Pacific type, indicating that a sufficiently continuous barrier extended for part of the time, at least, from central Newfoundland to the Scottish Highlands and thence to Scandinavia, and that the Appalachian geosyncline was continued to the north of this barrier (Figs. 1032, 1038). The Indian province was distinct from both the others. [Grabauʼs Fig. 1032 was a redrawn version On his paleogeographic maps he showed more information than others had done. He tried to indicate not only the coastlines, but also the locations of highlands, and the flow-directions of ancient rivers (Fig. 74), based on the preserved ...

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... Pacific type, indicating that a sufficiently continuous barrier extended for part of the time, at least, from central Newfoundland to the Scottish Highlands and thence to Scandinavia, and that the Appalachian geosyncline was continued to the north of this barrier (Figs. 1032, 1038). The Indian province was distinct from both the others. [Grabauʼs Fig. 1032 was a redrawn version On his paleogeographic maps he showed more information than others had done. He tried to indicate not only the coastlines, but also the locations of highlands, and the flow-directions of ancient rivers (Fig. 74), based on the preserved record of sedimentary deposits and fossils. Grabau's texts General Geology and ...

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... hypothesis that has received considerable attention attributes crustal deformation to slow-moving convection currents within a thick shell of the Earth (Fig. 295) [Fig. 81]. At first thought, it would appear that such currents are impossible, in view of abundant evidence proving rigidity in the Earth. It is urged, however, that a thick zone below the crust may be nearly devoid of strength, because of high temperature (p. 398). Some mathematical physicists agree that slow convection may operate in such a ...

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... continental fragment encounters resistance to movement and becomes deformed by folding and thrust faulting. This action causes thickening of the granitic shell; additional thickening is caused by frictional drag of the current as it turns obliquely downward, with the result that a large "root" is developed, made of the light granitic material (Fig. 295) [Fig. 81]. By the principle of isostasy, the buoyant effect of such a "root" would support a high mountain range (Fig. 273, p. ...

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... causes thickening of the granitic shell; additional thickening is caused by frictional drag of the current as it turns obliquely downward, with the result that a large "root" is developed, made of the light granitic material (Fig. 295) [Fig. 81]. By the principle of isostasy, the buoyant effect of such a "root" would support a high mountain range (Fig. 273, p. ...

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... the chapter on the Permian was still nearly identical to the one that Schuchert had written. Dunbar did add a comment that the wide Gondwanaland was "now discredited," but the land bridges were still part of the text. Of course, land bridges could not be shown on the map, since the Atlantic Ocean had been split in two, as in the 1941-edition (see Fig. ...

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... and Waage 1969, p. 82-83. In 1912 advanced the new theory of continental drift. He proposed that the southern continents and India are fragments of a great southern landmass centered about the South Pole in Paleozoic time -a land-mass which he called Pangea (Fig. 13-25). Thus he accounted for the glaciation and the associated Glossopteris flora. Then, he reasoned, this great landmass broke up into the present continental units which slowly drifted apart to their present positions. As supporting evidence, he pointed to the remarkable parallelism of the opposite margins of the Atlantic Ocean. Wegener's ...

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... theory seemed to many geologists at the time to be preposterous, it has recently gained wide acceptance and the paleomagnetic evidence appears now to offer a basis for reconciling the contrasts between the Permian climate of North America and Europe and that of the glaciation in the southern continents. The well known reconstruction by DuToit [1] (Fig. 13-25) was recently confirmed, in part, on the basis of comparison of the bedrock masses, the structural trends, and the glacial deposits ( Fig. 13-26). Admittedly more evidence from many sources is needed to establish the ideas suggested above or to disprove them, but we feel confident that it will be available in the next few ...

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... to offer a basis for reconciling the contrasts between the Permian climate of North America and Europe and that of the glaciation in the southern continents. The well known reconstruction by DuToit [1] (Fig. 13-25) was recently confirmed, in part, on the basis of comparison of the bedrock masses, the structural trends, and the glacial deposits ( Fig. 13-26). Admittedly more evidence from many sources is needed to establish the ideas suggested above or to disprove them, but we feel confident that it will be available in the next few ...

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... I have criticized this long-lived series of geology textbooks (Fig. 91), they were excellent in most ways, deserving the high praise they received. Their only major flaw was the doctrine of fixism. But that flaw was indeed major. It was also a conscious decision by the authors to let that flaw go uncorrected for over 40 ...