CHAPTER XVI.

WARM INTER-GLACIAL PERIODS IN ARCTIC REGIONS.

Cold Periods best marked in Temperate, and Warm Periods in Arctic, Regions.—State of Arctic Regions during Glacial Period.—Effects of Removal of Ice from Arctic Regions.—Ocean-Currents; Influence on Arctic Climate.—Reason why Remains of Inter-glacial Period are rare in Arctic Regions.—Remains of Ancient Forests in Banks’s Land, Prince Patrick’s Island, &c.—Opinions of Sir R. Murchison, Captain Osborn, and Professor Haughton.—Tree dug up by Sir E. Belcher in lat. 75° N.

In the temperate regions the cold periods of the glacial epoch would be far more marked than the warm inter-glacial periods. The condition of things which prevailed during the cold periods would differ far more widely from that which now prevails than would the condition of things during the warm periods. But as regards the polar regions the reverse would be the case; there the warm inter-glacial periods would be far more marked than the cold periods. The condition of things prevailing in those regions during the warm periods would be in strongest contrast to what now obtains, but this would not hold true in reference to the cold periods; for during the latter, matters there would be pretty much the same as at present, only a good deal more severe. The reason of this may be seen from what has already been stated in Chapter IV.; but as it is a point of considerable importance in order to a proper understanding of the physical state of things prevailing in polar regions during the glacial epoch, I shall consider this part of the subject more fully.

During the cold periods, our island, and nearly all places in the northern temperate regions down to about the same latitude, would be covered with snow and ice, and all animal and vegetable life within the glaciated area would to a great extent be destroyed. The presence of the ice would of itself, for reasons already explained, lower the mean annual temperature to near the freezing-point. The summers, notwithstanding the proximity of the sun, would not be warm, on the contrary their temperature would rise little above the freezing-point. An excess of evaporation would no doubt take place, owing to the increase in the intensity of the sun’s rays, but this result would only tend to increase the snowfall.[131]

During the warm periods our country and the regions under consideration would experience conditions not differing much from those of the present, but the climate would probably be somewhat warmer and more equable. The proximity of the sun during winter would prevent snow from falling. The summers, owing to the greater distance of the sun, would probably be somewhat colder than they are now. But the loss of heat during summer would be to a large extent compensated for by two causes to which we must here refer. (1.) The much greater amount of heat conveyed by ocean-currents than at present. (2.) Our summers are now cooled to a considerable extent by cold aërial currents from the ice-covered regions of the north. But during the period in question there would be little or no ice in arctic regions, consequently the winds would be comparatively warm, whatever direction they came from.

Let us next direct our attention to the state of things in the arctic regions during the glacial epoch. At present Greenland and other parts of the arctic regions occupied by land are almost wholly covered with ice, and as a consequence nearly destitute of vegetable life. During the cold periods of the glacial epoch the quantity of snow falling would doubtless be greater and the ice thicker, but as regards organic life, matters would not probably be much worse than they are at present. In fact, so far as Greenland and the antarctic continent are concerned, they are about as destitute of plant life as they can be. Although an increase in the thickness of the arctic ice would not greatly alter the present state of matters in those regions, yet what a transformation would ensue upon the disappearance of the ice! This would not only raise the summer temperature some twenty degrees or so, but would afford the necessary conditions for the existence of abundant animal and plant life. The severity of the climate of Greenland is due to a very considerable extent, as we have already seen, to the presence of ice. Get rid of the permanent ice, and the temperature of the country, _cæteris paribus_, would instantly rise. That Greenland should ever have enjoyed a temperate climate, capable of supporting abundant vegetation, has often been matter of astonishment, but this wonder diminishes when we reflect that during the warm periods it would be in the arctic regions that the greatest heating effect would take place, this being due mainly to the transference of nearly all the warm inter-tropical waters to one hemisphere.

It has been shown in Chapter II. that the heating effects at present resulting from the transference of heat by ocean-currents increase as we approach the poles. As a consequence of this it follows that during the warm periods, when the quantity of warm water transferred would be nearly doubled, the _increase of heat resulting from this cause would itself increase_ as the warm pole was approached. This effect, combined with the shortness of the winter in perihelion and the nearness of the sun during that season, would prevent the accumulation of snow. During summer, the sun, it is true, would be at a much greater distance from the earth than at present, but it must be borne in mind that for a period of three months the quantity of heat received from the sun at the north pole would be greater than that received at the equator. Consequently, after the winter’s snow was melted, this great amount of heat would go to raise the temperature, and the arctic summer could not be otherwise than hot. It is not hot at present, but this, be it observed, is because of the presence of the ice. When we take all these facts into consideration we need not be surprised that Greenland once enjoyed a condition of climate totally different from that which now obtains in that region.

It is, therefore, in the arctic and antarctic regions where we ought to find the most marked and decided evidence of warm inter-glacial periods. And doubtless such evidence would be abundantly forthcoming had these regions not been subjected to such intense denudation since the glacial epoch, and were so large a portion of the land not still buried beneath an icy covering, and therefore beyond the geologist’s reach. Only on islands and such outlying places as are not shrouded in snow and ice can we hope to meet with any trace of the warm periods of the glacial epoch: and we may now proceed to consider what relics of these warm periods have actually been discovered in arctic regions.

_Evidence of Warm Periods in Arctic Regions._—The fact that stumps, &c., of full-grown trees have been found in places where at present nothing is to be met with but fields of snow and ice, and where the mean annual temperature scarcely rises above the zero of the Fahrenheit thermometer, is good evidence to show that the climate of the arctic regions was once much warmer than now. The remains of an ancient forest were discovered by Captain McClure, in Banks’s Land, in latitude 74° 48′. He found a great accumulation of trees, from the sea-level to an elevation of upwards of 300 feet. “I entered a ravine,” says Captain McClure, “some miles inland, and found the north side of it, for a depth of 40 feet from the surface, composed of one mass of wood similar to what I had before seen.”[132] In the ravine he observed a tree protruding about 8 feet, and 3 feet in circumference. And he further states that, “_From the perfect state of the bark_, and the position of the trees so far from the sea, there can be but little doubt that they grew originally in the country.” A cone of one of these fir-trees was brought home, and was found to belong apparently to the genus _Abies_, resembling _A. (Pinus) alba_.

In Prince Patrick’s Island, in latitude 76° 12′ N., longitude 122° W., near the head of Walker Inlet, and a considerable distance in the interior in one of the ravines, a tree protruding about 10 feet from a bank was discovered by Lieutenant Mecham. It proved to be 4 feet in circumference. In its neighbourhood several others were seen, all of them similar to some he had found at Cape Manning; each of them measured 4 feet round and 30 feet in length. The carpenter stated that the trees resembled larch. Lieutenant Mecham, from their appearance and position, concluded that they must have grown in the country.[133]

Trees under similar conditions were also found by Lieutenant Pim on Prince Patrick’s Island, and by Captain Parry on Melville Island, all considerably above the present sea-level and at a distance from the shore. On the coast of New Siberia, Lieutenant Anjou found a cliff of clay containing stems of trees still capable of being used for fuel.

“This remarkable phenomenon,” says Captain Osborn, “opens a vast field for conjecture, and the imagination becomes bewildered in trying to realise that period of the world’s history when the absence of ice and a milder climate allowed forest trees to grow in a region where now the ground-willow and dwarf-birch have to struggle for existence.”

Sir Roderick Murchison came to the conclusion that all those trees were drifted to their present position when the islands of the arctic archipelago were submerged. But it was the difficulty of accounting for the growth of trees in such a region which led him to adopt this hypothesis. His argument is this: “If we imagine,” he says, “that the timber found in those latitudes grew on the spot we should be driven to adopt the anomalous hypothesis that, notwithstanding physical relations of land and water similar to those which now prevail, trees of large size grew on such _terra firma_ within a few degrees of the north pole!—a supposition which I consider to be wholly incompatible with the data in our possession, and at variance with the laws of the isothermal lines.”[134] This reasoning of Sir Roderick’s may be quite correct, on the supposition that changes of climate are due to changes in the distribution of sea and land, as advocated by Sir Charles Lyell. But these difficulties disappear if we adopt the views advocated in the foregoing chapters. As Captain Osborn has pointed out, however, Sir Roderick’s hypothesis leaves the real difficulty untouched. “A very different climate,” he says, “must then have existed in those regions to allow driftwood so perfect as to retain its bark to reach such great distances; and perhaps it may be argued that if that sea was sufficiently clear of ice to allow such timber to drift unscathed to Prince Patrick’s Land, that that _very absence of a frozen sea would allow fir-trees to grow in a soil naturally fertile_.”[135]

As has been already stated, all who have seen those trees in arctic regions agree in thinking that they grew _in situ_. And Professor Haughton, in his excellent account of the arctic archipelago appended to McClintock’s “Narrative of Arctic Discoveries,” after a careful examination of the entire evidence on the subject, is distinctly of the same opinion; while the recent researches of Professor Heer put it beyond doubt that the drift theory must be abandoned.

Undoubtedly the arctic archipelago was submerged to an extent that could have admitted of those trees being floated to their present positions. This, as we shall see, follows from theory; but submergence, without a warmer condition of climate, would not enable trees to reach those regions with their bark entire.

But in reality we are not left to theorise on the subject, for we have a well-authenticated case of one of those trees being got by Captain Belcher standing erect in the position in which it grew. It was found immediately to the northward of the narrow strait opening into Wellington Sound, in lat. 75° 32′ N. long. 92° W., and about a mile and a half inland. The tree was dug up out of the frozen ground, and along with it a portion of the soil which was immediately in contact with the roots. The whole was packed in canvas and brought to England. Near to the spot several knolls of peat mosses about nine inches in depth were found, containing the bones of the lemming in great numbers. The tree in question was examined by Sir William Hooker, who gave the following report concerning it, which bears out strongly the fact of its having grown _in situ_.

“The piece of wood brought by Sir Edward Belcher from the shores of Wellington Channel belongs to a species of pine, probably to the _Pinus (Abies) alba_, the most northern conifer. The structure of the wood of the specimen brought home differs remarkably in its anatomical character from that of any other conifer with which I am acquainted. Each concentric ring (or annual growth) consists of two zones of tissue; one, the outer, that towards the circumference, is broader, of a pale colour, and consists of ordinary tubes of fibres of wood, marked with discs common to all coniferæ. These discs are usually opposite one another when more than one row of them occur in the direction of the length of the fibre; and, what is very unusual, present radiating lines from the central depression to the circumference. Secondly, the inner zone of each annual ring of wood is narrower, of a dark colour, and formed of more slender woody fibres, with thicker walls in proportion to their diameter. These tubes have few or no discs upon them, but are covered with spiral striæ, giving the appearance of each tube being formed of a twisted band. The above characters prevail in all parts of the wood, but are slightly modified in different rings. Thus the outer zone is broader in some than in others, the disc-bearing fibres of the outer zone are sometimes faintly marked with spiral striæ, and the spirally marked fibres of the inner zone sometimes bear discs. These appearances suggest the annual recurrence of some special cause that shall thus modify the first and last formed fibres of each year’s deposit, so that that first formed may differ in amount as well as in kind from that last formed; and the peculiar conditions of an arctic climate appear to afford an adequate solution. The inner, or first-formed zone, must be regarded as imperfectly developed, being deposited at a season when the functions of the plant are very intermittently exercised, and when a few short hours of sunshine are daily succeeded by many of extreme cold. As the season advances the sun’s heat and light are continuous during the greater part of the twenty-four hours, and the newly formed wood fibres are hence more perfectly developed, they are much longer, present no signs of striæ, but are studded with discs of a more highly organized structure than are usual in the natural order to which this tree belongs.”[136]

Another circumstance which shows that the tree had grown where it was found is the fact that in digging up the roots portions of the leaves were obtained. It may also be mentioned that near this place was found an old river channel cut deeply into the rock, which, at some remote period, when the climate must have been less rigorous than at present, had been occupied by a river of considerable size.

Now, it is evident that if a tree could have grown at Wellington Sound, there is no reason why one might not have grown at Banks’s Land, or at Prince Patrick’s Island. And, if the climatic condition of the country would allow one tree to grow, it would equally as well allow a hundred, a thousand, or a whole forest. If this, then, be the case, Sir Roderick’s objection to the theory of growth _in situ_ falls to the ground.

Another circumstance which favours the idea that those trees grew during the glacial epoch is the fact that although they are recent, geologically speaking, and belong to the drift series, yet they are, historically speaking, very old. The wood, though not fossilized, is so hardened and changed by age that it will scarcely burn.