The Origin of Continents and Oceans/Chapter 6
CHAPTER VI
PALÆOCLIMATIC ARGUMENTS
This is not the place to discuss the whole of the problem of the climates of the past. Nevertheless, our reasoning forces us to give it a fleeting consideration, for only thus do the grounds become clear, which, from this standpoint, support the correctness of the displacement theory.
The present very undeveloped state of palæoclimatology is not the result of the absence of data on past climates. Their number is legion, although there are, frankly, many of them that we cannot yet certainly interpret, and unfortunately also many that have been interpreted incorrectly. The petrifactions of plants and animals form a great part of the evidence. The treeless tundra-flora beyond the limit of trees, coinciding with about the 10° C. isotherm of the warmest months, is usually clearly distinguished in the fossil state from the temperate forest flora. The latter can also be separated from the forests in the region of tropical rains by means of the annual rings in the wood, and sometimes also from the evergreen sub-tropical hard-leaved flora, which however only takes up a relatively small space in the present-day climatic system. Palms only occur in present-day climates, the coldest month of which does not have an average temperature below 6° C., and it is very probable that there was a similar temperature-limit for the palms of the past ages. Likewise corals are only found to-day in waters the temperature of which never falls below 20° C. Also no reptiles could have lived in past polar climates, since they produce no bodily heat, and likewise no earth-worms, since these cannot exist in frozen soil. But amphibia, and particularly fresh-water fishes, which utilize the warmth of the water, and mammals, which produce their own temperature, etc., could certainly do so. It is impossible to adduce here all the facts which can be employed to determine in what climate a given fossil fauna or flora lived. Of course, all these indications, if taken separately, are very uncertain, for both animals and plants yield examples of astonishing adaptation to a climate entirely foreign to the family concerned. But here, just as in the calculation of the path of a meteorite from a great number of inexact estimates, the individual data can be quite uncertain, often inverted, and, notwithstanding, give in their sum a very reliable result, when treated according to the law of the compensation of errors.
There still remain the inorganic evidences of climate, which have the advantage of not being able to adapt themselves. Boulder-clay, scratched detritus, and polished rock-surfaces, especially if they occur in a similar manner over great areas, denote the activity of land-ice, and therefore a polar climate. Coal, ancient peat-bogs, can form at the most different temperatures, but only if there is excess of rainfall compared with evaporation; conversely, salt deposits can only be formed in arid climates, that is, those with predominant evaporation. Thick unfossiliferous sandstones are to be considered as of desert formation, the red-coloured corresponding more to the hot deserts and the yellow-coloured rather to the more temperate ones (compare the red laterite of the tropics, the red earths of the subtropics, and the yellow clay of the temperate latitudes).
The enormous mass of facts which can be used in this way as fossil evidences of climate shows in an astonishing manner that in the past, in most regions of the earth, an entirely different climate prevailed from that of to-day. One especially striking example will now be given.
In Spitsbergen, which to-day with the severest polar climate lies under land-ice, forests of a greater variety of species of trees than are now to be found in Central Europe were still rustling in the Lower Tertiary. Not only were firs, pines and yews in existence, but also limes, beeches, poplars, elms, oaks, maples, ivy, sloes, hazel, hawthorn, guelder rose, ash, even such warmth-loving plants as water-lilies, walnut, swamp-cypress (Taxodium), immense sequoias, planes, chestnuts, ginkgo, magnolia, and the grape-vine. Therefore a climate must have prevailed in Spitsbergen similar to that of France to-day, and its average annual temperature must have been 20° C. higher than at present. And if we go further back into the earth’s history we find indications of a still greater warmth. In the Jurassic and lower Cretaceous sago-palms, which nowadays only occur in the tropics, ginkgo (only a solitary species to-day in China and South Japan), and tree-ferns flourished amongst others. Finally, in the Lower Carboniferous we find in Spitsbergen the tree-like Calamites, Lepidodendra, tree-ferns; in short, the same flora as that of the great coal-deposits of the Upper Carboniferous of Europe, which, in the judgment of those best qualified to form an opinion, was tropical. Therefore the climate of Spitsbergen must have been at that period about 30° C. higher than to-day.
This enormous variation of climate from a tropical to a polar one immediately suggests a displacement of the poles and of the equator, and therefore of the whole zonal system of climates. This view finds at once its confirmation in the fact that Central Africa, lying 90° of latitude south of Spitsbergen, underwent just such an enormous but exactly reverse change of climate in the same period of time. In the Carboniferous it was buried under a covering of land-ice; to-day it is in the region of equatorial rains. But 90° east of Central Africa, in the Sunda Archipelago, no variation of climate occurred; from the Tertiary at least this region had the same climate as to-day, which is shown in the unchanged preservation of numerous ancient plants and animals, as, for example, of the sago-palm or of the tapir. The northern part of South America was also in the same position as now, for, among other examples, the tapir has been preserved, whilst it is only found fossil in North America, Europe and Asia, except Further India, where it survives; it is not found at all in Africa.
Therefore it is not to be wondered at that in attempts to ascertain the rationale of former climatic changes, recourse was early and increasingly had to changes in the position of the poles. The parallel hypothesis of a sliding of the whole earth’s crust over its lower portions, adopted to comply with the necessity of keeping the axis of the earth unaltered in relation to the main mass, we can treat as identical with that of the shifting of the earth’s axis, as we have no means of deciding between them. We shall, therefore, for all purposes, understand by the wandering of the poles, a displacement of the poles on the earth’s surface, without reference to whether this was produced by a movement of the crust, or by a displacement of the axis in the interior of the earth, or by both together. Herder has already suggested such an explanation of the ancient climates in his ideas on the philosophical aspects of the history of the human race. It was more or less fully supported by numerous authors, as Sir John Evans (1876), Taylor (1885), Löffelholz von Colberg (1886), Oldham (1886), Neumayr (1887), Nathorst (1888), Hansen (1890), Semper (1896), Davis (1896), Reibisch (1901), Kreichgauer (1902), Golfier (1903), Simroth (1907), Walther (1908), Yokoyama (1911), Dacqué (1915), as well as recently by Eckhardt in numerous publications, the latest in 1921, and by E. Kayser in his well-known Lehrbuch der Geologie (1918), and by Koszmat (1921), among others.[1] This doctrine has always met with great opposition within the narrow circle of geological specialists and until the works of Neumayr and Nathorst the great majority of geologists totally rejected polar displacement. The picture changed after the publication of these works in so far that the adherents of the wandering of the poles became more numerous, though very slowly. To-day most geologists take the standpoint formulated in E. Kayser’s Lehrbuch, that the assumption of a great Tertiary displacement of the poles is in any case “difficult to avoid.” This can, indeed, be considered to be established, in spite of the remarkable bitterness with which some opponents challenge these ideas.
Although the grounds for the shifting of the poles (in certain periods of the earth’s history) are so compelling, nevertheless it cannot be denied that all previous attempts to fix the positions of the poles continuously throughout the whole geological succession have always led to self-contradiction, and indeed to contradiction of so grotesque a kind that it is not to be wondered at that the suspicion arises that the assumption of a shifting of the poles is built upon a fallacy. Such systematic attempts were undertaken in particular by Löffelholz von Colberg,[2] Reibisch[3] and Simroth,[4] Kreichgauer[5] and Jacobitti.[6] Unfortunately, Reibisch clothed his ideas, quite correct from the Cretaceous onwards, in the singular straight-jacket of a strict “pendulation” of the poles in an “orbit of swings,” which is probably false from the point of view of the laws of revolving bodies. In any case, it is without sufficient basis, and therefore leads to numerous contradictions of the observed facts. Simroth has collected a comprehensive amount of biological data which contains good evidence for the shifting of the poles, but which, however, is unable to prove the supposed strict regularity of the backward and forward swing. The purely inductive method is certainly the more correct, that is, to determine the position of the poles from fossil evidence of climates without any preconceived opinions on the subject. This method is adopted by Kreichgauer in his very exhaustive and clearly written book, even although he also relies on an insufficiently established dogma as to the arrangement of the mountain systems. Nearly all the investigations give practically the same result for the more recent periods, namely, a position of the North Pole at the beginning of the Tertiary in the neighbourhood of the Aleutian Islands, and from then a wandering towards Greenland, where it is to be found in the Quaternary. For these periods great relative discordances do not appear. But it is quite otherwise for the periods preceding the Cretaceous. Not only do the views of well-known authorities differ very widely, but as a consequence of the disregard of continental displacements the reconstructions lead to hopeless contradictions, indeed contradictions of such a kind that they form an absolute obstacle to any conceivable position of the pole at all.
The Permo-Carboniferous glacial deposits of the southern hemisphere form the most serious of those obstacles. These traces of ice-action are found on all the southern continents, sometimes with such surprising clearness that the direction of movement of the ice-masses can be read from the scratches on the polished surfaces of the rocks. These traces were first and best studied in South Africa, but they were then also discovered in Brazil, Argentina, in the Falkland Islands, in Togoland, in the Congo area, again in India, and in West, Central and East Australia.[7] If we merely place the South Pole in the conceivably best position (50° S. 45° E.) in the midst of these traces of ice, the remotest traces of land-ice in Brazil, India and Eastern Australia would possess a geographical latitude of not quite 10°, that is, a complete hemisphere of the earth was buried beneath the ice, and had therefore also the polar climate necessary for that purpose. The other hemisphere, however, the Carboniferous and Permian deposits of which are in most areas very well known, does not show sure traces of glaciation, but on the contrary at many places the remains of tropical vegetation. It need scarcely be said that this result is absurd. This has already been emphasized by numerous authors, probably most clearly by Koken,[8] to whom no other course seems to remain than to assume that all these masses of ice were formed at great heights above sea-level. But this hypothesis must appear just as impossible to the climatologists as that of F. v. Kerner, who states that it is a question of local anomalies of the distribution of heat caused by cold currents of the sea and such-like phenomena. It has therefore been urged by different authors, especially by A. Penck, that these facts render the assumption of displacements of the earth’s crust not improbable. Moreover the assumption that these traces were formed successively whilst the pole wandered or the earth’s crust was shifted beneath it, is wrecked, because no corresponding phenomena have been detected in the areas lying at the antipodes. If we allow the South Pole to wander from Brazil (of to-day) across Africa towards Australia, the velocity of this movement immediately excites well-founded distrust, and then the North Pole must trace a path from China to the east of Central America, where it must have left further traces behind. This is also in complete contradiction to the position of the Carboniferous and Permian equators and of the arid zones of those periods found by other means. The more exactly and completely we understand the whole evidence of the climates of those times, the more evident it becomes that, with the present positions of the continents, those climates cannot be adapted at all to any possible position of the poles and the climatic belts. It is not too much to say that this apparent inherent contradiction of observations among one another has absolutely crippled the development of palæoclimatology. All the above-quoted attempts to trace the position of the poles continuously throughout the geological succession must be wrecked on this rock.
The riddle of the Permo-Carboniferous glacial period now finds an extremely impressive solution in the displacement theory: directly those parts of the earth which bear these traces of ice-action are concentrically crowded together around South Africa, then the whole area formerly covered with ice becomes of no greater extent than that of the Pleistocene glaciation on the northern hemisphere. It is no longer merely a question of simplification which the displacement theory provides, it rather affords the first possibility of any explanation whatsoever.
In view of the great importance of these facts to the question of the correctness of the displacement theory, we will, in the following pages, attempt to take into account the most weighty of the remaining evidences of climate from the period under consideration, and see whether they adapt themselves, on the basis of the displacement theory, to a definite orientation of the climatic belts.
Let it be supposed that we have to reckon from the beginning that this very reduced ice-cap never existed in its complete extent, but has appeared successively in the different countries by the wandering of the South Pole. To be sure, the determination of the age at most places is not so exact that these relatively trifling differences of time can be safely detected geologically. But this time-displacement has also already been assumed on the geological side. Thus L. Waagen[9] suggests that the beds with Glossopteris lie above the boulder-clay in Africa and India, below in Australia. “Hence it is quite unambiguous, that the ice spread its mantle at an earlier period in India and South Africa, but at a later in Australia. We can thus establish a Carboniferous glacial epoch for Indo-Africa, for Australia a Permian.” In Argentina also, according to Gerth,[10] the sandstones with Glossopteris and Gangamopteris lie above the glacial deposits there. From this it might not be improbable that the most westerly traces found in Brazil, Togoland and the Congo had their origin in the lower Carboniferous. Since, again, ice phenomena are known in the Lower Devonian of South Africa,[11] the South Pole might have moved between the Lower Devonian to the Lower Carboniferous from Cape Colony to Loanda, then reversed, it would have moved in the Upper Carboniferous over from South Africa to the southern point of India and in the Permian to Australia. The corresponding path of the North Pole was completely in the Northern Pacific, and thus could produce no traces of ice worth mentioning. We shall now see how the remaining climatic evidences fit in with this. The most important are recorded in Fig. 17.
Let us first consider the distribution of the Glossopteris flora. The climatic character of this flora has been variously explained; to some it is a polar tundra-flora, to others it is only a temperate one. It will be generally admitted that it belongs to a colder climate than the normal tropical flora of the Carboniferous, which is yet to be described. But in my opinion we can go a step further, without risk of error, if we consider that it is a treeless flora, which will therefore occur outside of the limit of trees of that time. It is not necessary, of course, that the former limit of trees had the same temperature as that of to-day. The present limit of trees coincides with the 10° C. isotherm of the warmest months with an accuracy which at first sight is amazing.[12] This is easily explained by the fact that trees, by their height above the ground, are dependent on the temperature of the air which we can measure meteorologically, whilst the tundra-flora,
_-_figure_17.jpg)
Fig. 17.—Evidences of climate in the Permo-Carboniferous.
clinging as it does to the earth, makes use of the greater warmth of the soil and the atmosphere lying immediately above, heated by the uninterrupted day and night rays of the sun. Thus it secures a longer period of growth with temperatures of 10° or upwards right up to the poles. The Carboniferous limit of trees will have played a similar rôle even if it is possible that there was another limiting temperature for the very different flora of that time.[13] This “polar” flora of that period is found on the southern continents, as a rule in beds which lie partly below, partly above the glacial deposits and thus play a similar rôle to that of the interglacial beds of the European glacial period. But, as is to be expected, this flora extends beyond the limits of the ice, for it is found in Kashmir and the Eastern Himalayas as well as in Indo-China and in Borneo.
Wood with annual rings, which probably corresponds to the boreal or “snow-forest” climate of Köppen, has to my knowledge only been found at two places for this period, namely, by Arber in Australia (New South Wales) and by Halle on the Falkland Islands.
Finally, coal measures are known from the south polar region of that time, again in close connection with the Glossopteris flora and mostly lying directly on the Permo-Carboniferous moraines. They are known from Argentina (Lower Carboniferous), South Africa, Deccan and Australia. We are obviously dealing with the sub-polar peat-bogs of that period, which correspond exactly to our Quaternary and post-Quaternary peat-bogs in Europe (as well as those in Tierra del Fuego).
But these occurrences of coal are relatively unimportant compared with the great girdle of productive coal measures which extends through North America, Europe and Asia (China). The plant remains preserved point, according to H. Potonié,[14] to tropical forms, amongst other reasons, because of their rapid growth and the size of the leaf-frond, and on account of the absence of annual rings, the affinity with families that now have their home in the tropics, the frequency of tree- and climbing-ferns and the formation of the fructification on the stem itself, “cauliflorescence,” (which now only occurs in the tropics) in the Calamariaceæ, certain Lepidodendraceæ and the Sigillariaceæ. Some years ago it was thought by many (Ramann, Frech and others) that the formation of peat was connected with low temperature, and was impossible in the tropics because the processes of decomposition are much more powerful in those regions. This was quite natural so long as no recent bogs were known from the equatorial belt of rains. This, however, has been shown to be erroneous by the discovery of a great bog in the eastern portion of Sumatra, on the northern bank of the River Kampar; here the exclusion of atmospheric oxygen effected by the covering of water is sufficient to check decomposition and to produce peat. Since then further peat-bogs have been discovered in Ceylon and Equatorial Africa. Therefore the former very lively discussion on the tropical nature of our coal measures can be considered as having been settled. As is shown by Fig. 17, this girdle of coal measures lies exactly on the great circle which occurs about 90° from the centre of the area of glaciation. That this happy solution is only rendered possible by the displacement theory is shown by the annexed map of Kreichgauer, which is given for the sake of comparison (Fig. 18). Just as in the case of the
_-_figure_18.jpg)
Fig. 18.—Carboniferous folds and position of the equator, after Kreichgauer.
equator of the early Tertiaries, the Carboniferous equator consists of a girdle of mountain folding (“Karbon-ring” of Kreichgauer), which certainly points to especially favourable conditions for the formation of bogs, since it contains the great coalfields referred to. It will be noticed, however, that the belt of folding of Kreichgauer deviates enormously in North America, and also in Australia, from the “Karbon-äquator,” and that in South America, which is cut through by the latter, such a mountain region is quite absent. Also the position of the equator does not fit in with the climatic evidences. By the comparison of this map with that drawn from the standpoint of the displacement theory (Fig. 17), it is clear that the zone of equatorial rains can only be truly represented in the latter.
The chronological sequence of the great occurrences of coal harmonizes with the position of the South Pole derived from the glacial deposits. Tropical coal occurs in the Carboniferous, also in Spitsbergen, and according to Andersson, amounts to more than two-thirds of its total coal resources. But this coal is Lower Carboniferous (Culm). It lies about 90° from the traces of ice-action in Togoland, the Congo and Brazil, the formation of which we also placed in the Lower Carboniferous. The plant remains, here also, are tropical, just as the corresponding ones in North-east Greenland at 81° latitude and on Melville Island. We are manifestly still dealing with the zone of equatorial rains of the Lower Carboniferous. On the other hand, the coals of the chief girdle of coal measures are in the main later; the Chinese coals are partly placed in the Lower Carboniferous (Shantung and Southern Szechwan), partly in the Upper Carboniferous (northern slopes of the River Nanshan), partly in the Permian (Shansi, Chihli, Manchuria), or even in the Trias (Hunan).[15] In Europe the Lower Carboniferous coals extend southwards as far as Scotland, Chemnitz and Moscow; the Middle Carboniferous as far as Brittany and Upper Silesia; and the Upper Carboniferous to western Auvergne, Baden, Brenner and Laibach. Even the Permian contains coal in France, Thuringia, Saxony and Bohemia, though only in the lowest beds immediately above the Carboniferous. The main mass of European coal is Upper Carboniferous, just as in North America, where likewise a shifting of the coal area from north to south is recognizable (Lower Carboniferous, New Brunswick to Virginia; Upper Carboniferous, Ohio to Alabama). But by the time of the Middle Permian indications of an arid area occur in place of coal. We therefore see in Europe a shifting of the coal-forming zone from Spitsbergen (in the Lower Carboniferous) towards Central Europe (Upper Carboniferous and lowermost Permian). No coals are known from the Upper Permian.
This displacement of the zone of equatorial rains shown by the occurrence of coal is beautifully confirmed by the similar shifting of the following northern arid zone, which is especially well shown by the deposits of rock-salt and gypsum.[16] Whilst it is in the Permian, the most recent formation considered here, that coal is absent, salt deposits are lacking in the oldest, that is, in the Lower Carboniferous. Rock-salt and gypsum are first found in the Upper Carboniferous of the Eastern Urals, north of the girdle of coal measures, and also already in Newfoundland, where it is above and therefore succeeding in time the coal horizons. Spitsbergen, according to Semper, had already a dry climate then. Thus the arid zone followed directly on the heels of the formation of coal. But the greatest salt and gypsum deposits first occur in the Permian, and indeed first in the Upper Permian, in which coals had already vanished, i.e. in Eastern Russia, North Germany, in the Southern Alps, and in the United States. Thus the formation of salt also advanced in this period of time from north to south, from Spitsbergen (in the Lower Carboniferous) to the Southern Alps (in the Upper Permian), and so followed after the formation of coal. Scarcely a doubt can therefore exist in this case that we are dealing with the northern arid zone.
In the above we have confined ourselves to the more important evidences of the climate of this period, and it must be allowed that, on the basis of the displacement theory, these can be presented with great logical consistency. It would carry us too far to deal here, completely, with the less important climatic evidences. As far as can be seen, the latter also fit themselves, without exception, into the picture. A few examples are given. The average size of the wings of insects in the Lower and Middle Carboniferous, according to Handlirsch, amounted to 51 mm.; in the Upper Carboniferous and Permian, however, only 20 to 17 mm. This is in good agreement with the fact that the equator had its most northerly position in the Lower Carboniferous, and that Europe fell into the northern arid zone in the Permian. In the Lower Carboniferous, coral reefs are not only known from Cantabria and the Carnic Alps, but also from Belgium, England and Ireland; from the Middle and Upper Carboniferous of North America (Middle Carboniferous: Indiana, Illinois, Alabama; Upper Carboniferous: Kansas to Texas).[17]
On the other hand, the Permian of Timor only contains individual corals, and not those forming reefs in warm waters.
According to Gerth, the Permian of Uruguay and Southern Brazil shows a rapid increase of temperature. Mesosaurus already appeared there, and limestone and dolomite beds are found among shales, a fact which always denotes warm water. The Permo-Carboniferous “Red Beds” in western North America fit extraordinarily well in our picture, since they manifestly belong to the desert region of the northern arid zone. That great parts of Africa changed in the period from the Carboniferous to the Permian from the zone of temperate rains into the southern arid zone harmonizes very well with the conclusion of Passarge, who assumed a long desert period in the Mesozoic in order to explain the present-day surface features of that area.[18]
Let us throw a glance for comparison on the distribution of climate in the Devonian period preceding the Carboniferous, but bear in mind the inexactitude of the groundwork of our maps, caused by the Carboniferous mountain folds not being smoothed out. It has already been mentioned that Lower Devonian traces of ice-action are known from South Africa. On the other hand, traces of the northern desert zone are seen in the Old Red desert formation, (already considered in Chapter IV, dealing with the geological arguments), in North America, Greenland, Spitsbergen and Northern Europe, and which also contains salt and gypsum deposits in North America and the Baltic Provinces. Thus it proves itself a good witness of the presence of the arid zone. The equator of the Lower Devonian must have had a similar orientation to that of the Upper Carboniferous. The Devonian coals at Neunkirchen in the Eifel consequently belong to the equatorial zone of rains, and the Devonian coral reefs in England, Belgium, Southern France, North-west Germany, Silesia and the Alps fit in very well with this view. The greatest part of Africa (Lower Nubian Sandstone) and Brazil lay in the southern arid zone. However, we cannot go into any further details here, it being sufficient to have shown that when the positions of the poles have been found for the Carboniferous and Permian a connection with those of the Devonian is not lacking.
The whole of these evidences of the climate of the Permo-Carboniferous period give such a convincing picture of the climatic zone prevailing then that I do not see how this conception of the position and direction of movement of the poles can be dismissed. In this way these evidences become a strong proof of the accuracy of the displacement theory.
The Carboniferous period has been deliberately chosen for the foregoing discussion, since it shows most clearly the simplification produced by the displacement theory. It is now clear that the rôle of this theory becomes greater the further we go back into the earth’s history, since at the same time the displacements of the continents become greater and greater in comparison with their present position. Also the Carboniferous is the most ancient period in which the displacement theory has been yet worked out. On account of this also, the criteria for the displacement theory which we have obtained from the study of the position of the poles for the later periods are of gradually decreasing importance. If we would completely test the state of affairs, we must also determine the position of the climatic belts for the succeeding periods up to the Quaternary with the same thoroughness as for the Permo-Carboniferous, and in each case attempt to discover how far improvements result from the application of the displacement theory. This work has not yet been carried out with the required care, but I hope to be able to accomplish it in the not far distant future in another publication written in conjunction with W. Köppen.[19] The results of a provisional survey of only the most striking evidences of climate which were set out in detail in the previous (second) edition of this book are here reproduced so as to give a general idea of their nature. It is to be anticipated that the proposed detailed work will lead to a modification of these figures, yet no ground exists for supposing that they will be radically changed. I obtain the following position of the North and South Poles with reference to the present system of co-ordinates, with Africa supposed to be stationary:—| North Pole. | South Pole. | Germany. | ||||||||
|
90° N. | 0— | 90° S. | 0— | 50° N. | |||||
|
70° N. | 010° W. | 70° S. | 170° E. | 69° N. | |||||
|
90° N. | 0— | 70° S. | 0— | 54° N. | |||||
|
67° N. | 172° W. | 67° S. | 008° E. | 37° N. | |||||
|
58° N. | about | 180° W. | 58° S. | about | 000 | 29° N. | |||
|
45° N. | about„ | 180° W. | 45° S. | about„ | 000 | 15° N. | |||
|
50° N. | about„ | 180° W. | 50° S. | about„ | 000 | 20° N. | |||
|
48° N. | 140° W. | 48° S. | 040° E. | 19° N. | |||||
|
69° N. | 170° W. | 69° S. | 010° E. | 36° N. | |||||
PermianTrias Average
|
50° N. | 130° W. | 50° S. | 050° E. | 26° N. | |||||
Permian Position
| ||||||||||
|
25° N. | 155° W. | 25° S. | 025° E. | 03° S. | |||||
|
30° N. | 140° W. | 30° S. | 030° E. | 15° N. | |||||
The figures in the last column indicate in which geographical latitude any place in Germany in the present latitude 50° might be found in the course of geological time. This is illustrated in Fig. 19 below.
The Quaternary glaciation of North Europe and North America will now be given a brief treatment, but only so far as it offers facts on behalf of the displacement theory. As is shown by Fig. 20, according to the displacement theory the continents immediately adjoined each other at the beginning of the Quaternary. The separation may have taken place at the period of maximum glaciation, or, just as possibly, shortly before. In any case, the distance between the blocks was not of any considerable importance when the glaciation was at its maximum;
_-_figure_19.jpg)
Fig. 19.—The position (latitude) of Central Europe in the course of the earth's history.
on the other hand, the blocks must have been separated considerably by the time of the last glaciation. This conclusion is derived from the consideration of the westerly directed gradient of the strand-lines of Western Norway. It had already been seen that the outermost terminal moraines in Europe and North America join up smoothly. But what is most interesting is the extensive diminution of the total glaciated area according to the displacement theory. However much one may have thought about the thorny question of the cause of the glacial period, it must in any case be admitted that the displacement theory does not make the comprehension of the phenomenon more difficult, but more simple. Still another interesting detail of the phenomena of the Quaternary glaciation may be mentioned.
_-_figure_20.jpg)
Fig. 20.—Reconstruction of the continental blocks for the Great Ice Age.
According to A. Penck, the Pleistocene snow-line lay 500 to 600 m. lower in Tasmania than in New Zealand. This is very difficult to understand, because of the present nearly equal latitudes of the two localities. The displacement theory removes this difficulty, for, according to it, Tasmania then lay considerably farther south than New Zealand.
- ↑ For the literature up to 1918, see Th. Arldt, “Die Ursachen der Klimaschwankungen der Vorzeit, besonders der Eiszeiten,” Zeitschr. f. Gletscherkunde, 11, 1918.
- ↑ Carl Freiherr Löffelholz von Colberg, Die Drehungen des Erdkruste in geologischen Zeiträumen. Eine neue geologisch-astronomische Hypothese, Munich, 1886; second, very much enlarged, edition, 1895.
- ↑ P. Reibisch, Ein Gestaltungsprinzip der Erde, 27. Jahresber. d. Ver. Erdkunde zu Dresden, pp. 105–124, 1901. Second part (containing only unimportant supplements), Mitt. Ver. Erdk. Dresden, 1, pp. 39–53, 1905. Third part, ‘‘ Die Eiszeiten,” ibid, 6, pp. 58–75, 1907.
- ↑ H. Simroth, Die Pendulationstheorie. Leipzig, 1907.
- ↑ Kreichgauer, Die Äquatorfrage in der Geologie. Steyl, 1902.
- ↑ E. Jacobitti, Mobilità dell’Assa Terrestre, Studio Geologico. Turin, 1912.
- ↑ Compare the map in Dacqué, Grundlagen und Methoden der Paläogeographie. Jena, 1915.
- ↑ E. Koken, “Indisches Perm und die permische Eiszeit,” Festband d. N. Jahrb. f. Min., 1907.
- ↑ L. Waagen, Unsere Erde, p. 437. Münich, Allg. Verl.-Ges., n.d.
- ↑ H. Gerth, “Die Fortschritte der geologischen Forschung in Argentinien und einigen Nachbarstaaten während des Weltkrieges,” Geol. Rundsch., pp. 74–87, 1921.
- ↑ H. Cloos, “Geologische Beobachtungen in Südafrika. III. Die vorkarbonischen Glazialbildungen des Kaplandes,” Geol. Rundsch., 6, Heft 7/8, 1916.
- ↑ W. Köppen, “Baumgrenze und Lufttemperatur,” Petermann’s Mitt., pp. 201–203, 1919.
- ↑ Thus nowadays a fern grows in Greenland at the edge of the ice. But the limit of tree-ferns is to-day 30° to 50° in the southern hemisphere. “The most southerly points where fern-trees occur are Tasmania and the South Island of New Zealand with Auckland. In South Brazil Dicksonia sellowiana and Alsophila procera extend to S. Paulo; in North Argentina to Misiones; in Cape Colony Hemitelia capensis is the last stage towards the south.” (Robert Potonié, Paläoklimatisches im Lichte der Paläobotanik, Naturw. Wochenschr., June 26, 1921, p. 383.)
- ↑ H. Potonié, “Die Tropensumpfflachmoornatur der Moore des productiven Karbons,” Jahrb. d. Kgl. Preusz. Geol. Landesanstalt., 33, Teil 1, H. 3, Berlin, 1909.—H. Stremme, Über tropische Moore, “Gæa,” 45, No. 11, 1909.
- ↑ F. Frech, “Die Kohlenvorräte der Welt,” Finanz- und Volkswirtschalftl. Zeitfragen, Heft 43. Stuttgart, 1917.
- ↑ Information about deposits of rock-salt, which are so important for palæoclimatological purposes, is given by J. O. Freiherr von Buschmann, Das Salz, Vol. 2. Leipzig, 1906. Unfortunately the geological data as to their age are often quite incomplete.
- ↑ Th. Arldt, Paläogeographie, 2. Leipzig, 1921.
- ↑ S. Passarge, “Die Inselberglandschaft im tropischen Afrika,” Naturw. Wochenschr., N.F., 3, p. 657, 1904.
- ↑ This work has since been completed, and is now in the press under the following title: W. Köppen and A. Wegener, Die Klimate der geologischen Vorzeit, Berlin. (Borntraeger).