Some Salient Points in the Science of the Earth

by Sir John William Dawson

The question of the supply of light to an Arctic flora is much less difficult than some have imagined. The long summer day is in this respect a good substitute for a longer season of growth, while a copious covering of winter snow not only protects evergreen plants from those sudden alternations of temperature which are more destructive than intense frost, and prevents the frost from penetrating to their roots, but by the ammonia which it absorbs preserves their greenness. According to Dr. Brown, the Danish ladies of Disco long ago solved this problem.[107] He informs us that they cultivate in their houses most of our garden flowers, as roses, fuchsias, and geraniums, showing that it is merely warmth, and not light that is required to enable a subtropical flora to thrive in Greenland. Even in Canada, which has a flora richer in some respects than that of temperate Europe, growth is effectually arrested by cold for nearly six months, and though there is ample sunlight there is no vegetation. It is indeed not impossible that in the plans of the Creator the continuous summer sun of the Arctic regions may have been made the means for the introduction, or at least for the rapid growth and multiplication, of new and more varied types of plants. It is a matter of familiar observation in Canada that our hardy garden flowers attain to a greater luxuriance and intensity of colour in those more northern latitudes where they have the advantage of long and sunny summer days.

[107] Florula Discoana, Botanical Society of Edinburgh, 1868.

Much, of course, remains to be known of the history of the old floras whose fortunes I have endeavoured to sketch, and which seem to have been driven like shuttlecocks from north to south, and from south to north, especially on the American continent, whose meridional extension seems to have given a field specially suited for such operations.

This great stretch of the western continent from north to south is also connected with the interesting fact that, when new floras are entering from the Arctic regions, they appear earlier in America than in Europe; and that in times when the old floras are retreating from the south, old genera and species linger longer in America. Thus, in the Devonian and Cretaceous new forms of those periods appear in America long before they are recognised in Europe, and in the modern epoch forms that would be regarded in Europe as Miocene still exist. Much confusion in reasoning as to the geological ages of the fossil flora has arisen from want of attention to this circumstance.

What we have learned respecting this wonderful history has served strangely to change some of our preconceived ideas. We must now be prepared to admit that an Eden might exist even in Spitsbergen, that there are possibilities in this old earth of ours which its present condition does not reveal to us; that the present state of the world is by no means the best possible in relation to climate and vegetation; that there have been and might be again conditions which could convert the ice-clad Arctic regions into blooming paradises, and which, at the same time, would moderate the fervent heat of the tropics. We are accustomed to say that nothing is impossible with God; but how little have we known of the gigantic possibilities which lie hidden under some of the most common of His natural laws.

Yet these facts have been made the occasion of speculations as to the spontaneous development of plants without any direct creative intervention. It would, from this point of view, be a nice question to calculate how many revolutions of climate would suffice to evolve the first land plant; what are the chances that such plant would be so dealt with by physical changes as to be preserved and nursed into a meagre flora like that of the Upper Silurian or the Jurassic; how many transportations to Greenland would suffice to promote such meagre flora into the rich and abundant forests of the Upper Cretaceous, and to people the earth with the exuberant vegetation of the early Tertiary. Such problems we may never be able to solve. Probably they admit of no solution, unless we invoke the action of a creative mind, operating through long ages, and correlating with boundless power and wisdom all the energies inherent in inorganic and organic nature. Even then we shall perhaps be able to comprehend only the means by which, after specific types have been created, they may, by the culture of their Maker, be "sported" into new varieties or sub-species, and thus fitted to exist under different conditions, or to occupy higher places in the economy of nature.

Before venturing on such extreme speculations as some now current on questions of this kind, we would require to know the successive extinct floras as perfectly as those of the modern world, and to be able to ascertain to what extent each species can change, either spontaneously or under the influence of struggle for existence, or expansion under favourable conditions, and under Arctic semi-annual days and nights, or the shorter days of the tropics. Such knowledge, if ever acquired, it may take ages of investigation to accumulate. In any case the subject of this paper indicates one hopeful line of study with the object of arriving at some comprehension of the laws of creation.

While the facts above slightly sketched impress us with the grand progress of the vegetable kingdom in geological time, they equally show the persistence of vegetable forms as compared with that of the dead continental masses and the decay of some forms of life in favour of the introduction of others.

When we find in the glacial beds the leaves of trees still living in North America and Europe, and consider the vicissitudes of elevation and submergence of the land, and of Arctic and temperate climates which have occurred, we are struck with the persistence of the weak things of life, as compared with the changeableness of rocks and mountains. A superficial observer might think the fern or the moss of a granite hill a frail and temporary thing as compared with solid and apparently everlasting rock. But just the reverse is the case. The plant is usually older than the mountain. But the glacial age is a very recent thing. We have facts older than this. As hinted in a previous paper, in the Laramie clays associated with the Lignite beds of North-western Canada—beds of Lower Eocene or early Tertiary age—which were deposited before the Rocky Mountains or the Himalayas had reared their great peaks and ridges, and at a time when the whole geography of the northern hemisphere was different from what it is at present—are remains of very frail and delicate plants which still live. I have shown that in these clays there exist, side by side, the Sensitive Fern, Onoclea sensibilis, and one of the delicate rock ferns, Davallia tenuifolia.[108] The first is still very abundant all over North America. The second has ceased to exist in North America, but still survives in the valleys of the Himalayas. These two little plants, once probably very widely diffused over the northern hemisphere, have continued to exist through the millenniums separating the Cretaceous from the present time, and in which the greater part of our continent was again and again under the sea, in which great mountain chains have been rolled up and sculptured into their present forms, and in which giant forms, both of animal and plant life, have begun, culminated and passed away. Truly God hath chosen the weak things of the world to confound those that are strong.