ON THE VALUE OF THE FOSSIL FLORAS OF THE ARCTIC REGIONS AS EVIDENCE OF GEOLOGICAL CLIMATES.1

By Prof. A. G. NATHORST, of Stockholm.

Translated from the French original' by E. A. NEWELL ARBER, M. A., F. G. S.

Among the problems which are constantly called to mind during geological explorations in the Arctic regions, that of the climates of the past naturally demands special attention. The contrast between the present and the past is there more striking than in any other region. Beneath the snow and ice bordering the Arctic Sea one marvels to find, for example, large corals in beds belonging to the Carboniferous system, or again the remains of saurians, ammonites, or nautiloids in those of Triassic age. But when one bears in mind the extreme richness of the invertebrate fauna of the Arctic Seas to-day, when one remembers the colossal whales which find their subsistence in these waters, one may be inclined to ask if it has not been an error to conclude, from the occurrence of the fossils above mentioned, that the climate was formerly more genial than it is to-day. Should we not be underestimating the creative power of life if we imagine that, among the saurians, the ammonites, and the nautiloids, no species has been able to develop which was adapted to life in the Arctic Seas? If the reindeer and the musk ox were extinct, who would imagine that these beasts were able to flourish on the scanty vegetation of the high parallels north of 80° of latitude? And who would suppose that such monsters as the mammoth and the woolly rhinoceros could find sufficient nourishment in the poor vegetation of the tundras or the coriferous forests? Such examples teach prudence; there is certainly no question which requires so much caution as the problem of deducing from the faunas of the past the climatic conditions under which they flourished.

This remark applies with equal force to the floras. Although to-day the cycads only occur in warm regions, it would be an error

1 A paper read before the Eleventh International Geological Congress on Aug. 25, 1910. "Sur la valeur des flores fossiles des régions arctiques comme preuve des climats géologiques," Stockholm, 1910. Also in Compt. Rend. Eleventh Intern. Geol. Congr., Stockholm, 1912. Reprinted by permission from the Geological Magazine, London, Decade V, vol. 8, No. 563, pp. 217-225, May, 1911.

The English translation has been revised by Prof. Nathorst, and references added.

to conclude that the cycadophyta of the past have always flourished under similar conditions. On the contrary, we must admit that during the Mesozoic period, when these plants were abundant, it would no doubt have been possible to find several species which had adapted themselves to an Alpine climate if such a one had then existed. And if, since then, the differentiation of climates has begun to make itself felt, it would be again a case of overlooking the creative power of life if we assumed that none of the species of cycadophytes were able to adapt themselves to a temperate climate in the Polar regions. Again we meet with difficulties, even when we study the plants of the Tertiary period, which are assigned to genera still living. Our common juniper (Juniperus communis, Linn.), which exists in northern Europe as far north as the North Cape, exceeds by 20 to 25 degrees of latitude, in the Eastern Hemisphere, the northern limit, not only of the other species of this genus, but also the whole family of the cupressineæ. Now, if one imagined that the common juniper were extinct, one would naturally draw conclusions relative to the fossil remains from the distribution of the other species, and one would consequently suppose that it lived under a climate much warmer than is actually the case. One would scarcely imagine that we were concerned with a plant adapted not only to temperate but also to Arctic climates. (One finds the juniper, on the western side of Greenland, up to the sixty-fourth parallel.)

These examples counsel prudence, and the matter should be treated with judgment and circumspection. But, even if it is necessary to make reservations, when one seeks to determine from the fossil plants the nature of the former climates in the Arctic regions, at least one can not doubt that they were distinctly warmer than that of the present day. The difficulty of explaining these former climates, especially when one has to take into consideration the length of the winter night, is without doubt the reason which has led some scientists to evade the question, instead of seeking to solve it. It is indeed a case of evading the question when it is boldly asserted that the plantremains, on which Heer has based his theories of ancient Arctic climates, have been drifted by marine currents to the places where they have been found.

It is not to be disputed that plant débris may be transported in water for a very great distance without being damaged, provided that they are carried at a sufficient depth to escape the influence of the movements of the surface layers of the water. When Agassiz was engaged in dredging on the American coasts, he found that the bottom of the sea-sometimes to a depth of nearly 3,000 meters-was covered with plant débris, such as wood, branches, leaves, seeds, and fruits,

10. Heer, Flora fossilis arctica, vols. 1-7, Zürich, 1868-1883.

in all stages of decay. Also, in certain places, these remains were still fairly abundant at a distance of 1,100 to 1,200 kilometers from the shore. This distance corresponds to about 10 degrees of latitude. It is thus proved that the remains of plants may be transported for very considerable distances. But this is true only of marine deposits. If we are concerned with fresh-water sediments, the example given has no bearing on the case.

One might, however, reasonably suppose that a river, flowing in the direction of the meridian from south to north, might have carried from the southern regions leaves and other fragments of vegetation which became buried in some deposit of the stream itself, or of a lake, which it traversed, or of its delta. This is a possibility which must not be neglected, but on the other hand it must not be treated as though it were an ascertained fact, since we do not know how far it applies to the case in point.

The fact is, it is puerile to attempt to draw conclusions as to the ancient climates of the Arctic regions, before the nature of the deposits in which the fossil plants have been found has been ascertained. It is especially important that an attempt should be made to answer the question, Did the plants once flourish in the neighborhood of the deposits in which they are found, or were they transported from far-away lands? It is this question which an attempt will here be made to solve, by furnishing a concise résumé of the principal beds containing fossil plants in the Arctic regions.

In Bear Island,' and in Ellesmere Land,' beds extremely rich in plant remains are met with belonging to the Devonian system. The fossil plants of Bear Island occur in the series of beds which also include several seams of coal. Beneath the coal, which is composed essentially of the bark and trunks of Bothrodendron, one finds, as elsewhere, bituminous schists containing roots, and from this one can show that the plants of which we speak flourished, at least in part, in situ. This is likewise proved by the actual nature of the plants, as much in the older beds with Archæopteris fimbriata Nath., as in the more recent with Pseudobornia ursina Nath. The latter species has been found with large stems or rhizomes, as well as very small ones, only a few millimeters in diameter, to which extremely delicate, almost membranous, leaves are still attached. It is hence quite certain that there is here no question of the plants having come from distant regions. The materials have not been sorted out. One sees a medley of branches, small and large, and the perfection of the

1 A. G. Nathorst, "Zur Oberdevonischen Flora der Bären Insel:" Kongl. Svenska Vet.-Akad. Handl., vol. 36, No. 3, Stockholm, 1902.

2 Id., "Die Oberdevonische Flora des Ellesmere Landes:" Rep. 2nd Norweg. Arctic Exped. in the Fram vol. 1, Christiania, 1904.

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preservation of their delicate leaves demonstrate conclusively that they have not undergone transportation from afar. The same applies to Archæopteris fimbriata. The beds of coal, the clay with rootlets, and the very nature of the plants themselves, all point to the same conclusion, namely, that we have here a flora which flourished in part on the very spot where it is now found.

As I have already pointed out in my description of the Devonian flora of Ellesmere Land, one arrives at the same conclusions here also, and it is unnecessary to enter into further details.

In the Arctic regions, culm deposits, yielding fossil plants, are known from Spitsbergen,' from the northeast of Greenland, and probably from the south of Melville Island, in the Arctic Archipelago of America.

We will here concern ourselves only with Spitsbergen, although it may be mentioned in passing that the flora of the culm discovered by the Danish expedition to Northeast Greenland, in latitude 81° north, consists of nearly the same species as that of Spitsbergen. The latter flora has been observed in many localities up to 79° of latitude. It is characterized by the presence of Stigmaria, with appendicular organs radiating in all directions, still in continuity, and penetrating the clay beneath. We are thus able, in several places, to observe the presence of Stigmaria in situ, which furnishes undeniable evidence of the fact that the plants lived in the place where we now find them. The stems of Lepidodendron found in the same place have a diameter of at least 40 cm. It would be superfluous to give other examples, for one can scarcely doubt that the plants of the culm have flourished in the very place in which they are now found, or in its vicinity.

On the other hand, the observations which relate to the Triassic plants of Spitsbergen and eastern Greenland are somewhat different. The latter ones belong to the Rhætic Series and include several species of Pterophyllum, Podozamites, Cladophlebis, etc. In Spitsbergen one finds them as far north as 78°. Neither there nor in Eastern Greenland, where one meets with them between the 70th and 71st parallel, are they associated with beds of coal, but the manner in which they occur in Greenland indicates that in no case have they traveled from very distant localities. One has not with certainty observed any marine petrifactions associated with the plants, but it has not yet been clearly determined whether the Triassic beds with fossil plants of Spitsbergen are of marine or of freshwater origin.

1 A. G. Nathorst, "Zur Paläozoischen Flora der Arctischen Zone:" Kongl. Svenska Vet.-Akad. Handl., vol. 26, No. 4; Stockholm, 1894.

2 Id., "Contributions to the Carboniferous Flora of Northeastern Greenland:" Meddelelser om Grönland, vol. 43; Copenhagen, 1911.

N. Hartz, "Planteforsteninger fra Cap Stewart i Östgrönland:" Meddelelser om Grönland, vol. 19; Copenhagen, 1896.