vated, into which the surges have rolled with the deafening reverberations of a sea-coast "purgatory." The principal plateau of the island is limited at nearly all points by an abrupt wall dropping down into the deep waters of the lake. Here is a beetling cliff, one hundred and forty-five feet high, called "Lover's Leap," connected with a sentimental Indian legend. In another place is "Chimney Rock," one hundred and thirty-one feet high, and in another, "Robinson's Folly." At "Arched Rock" (Fig. 86),

LGESIAL-BARRITT.

Fig. 86. Arched Rock, Mackinac Island.

on the eastern side, towering one hundred and forty feet above the lake, the fierce waves, unable to reach the solid and unyielding brow of the precipice, have mined beneath it, perforating the limestone wall; and a natural bridge hangs there, with one end resting on a winged abutment stretching toward the lake. All round the walls of this castellated and charming isl and the recording waves have left their hieroglyphs, from the water's edge to the battle.

ments, and he who can read the language may ponder there the vicissitudes of the ages.

While, during the high tides of the lakes, the erosive waves were gnawing at the rocks of Mackinac and Ohio, the waters of Lake Michigan, in a quieter mood, were performing a work equally enduring and peculiar. Here we find our attention challenged by the question of prairie origin and prairie features, but the views to be presented will be held in abeyance until a chapter on a subsidiary topic shall have been interposed.

L 2

CHAPTER XXIII.

VITALITY OF BURIED VEGETABLE GERMS.

VENTURE here to enunciate a view which to many may appear incredible. For some years past I have been inclined to believe that the germs of vegetation which flourished upon our continent previous to the reign of ice, and many of which must have been buried from twenty to one hundred feet beneath the surface of the glacial rubbish, may have retained their vitality for thousands of years, or even to the present time. There are not a few indications that vegetable germs are capable of such preservation, and not a few that they thus exist in the ancient drift. The consequences of such remarkable preservation possess a geological importance so novel and interesting that I am sure the reader will be pleased with a view of the facts bearing upon the doctrine.

Many familiar facts may be cited which certainly have a significance far greater than has been generally suspected, and which tend to show that the seeds of vegetation are reposing in a dormant state in our ordinary soils and subsoils. Nothing is a more common observation than to see plants making their appearance in situations where the same species was previously unknown, or for a long time. unknown, and under circumstances such that the supposition of a recent distribution of seeds is quite precluded.

The sudden appearance of unwonted species frequently occurs when a change is produced in the physical condition of the soil. Left to Nature, certain perennial grasses secure almost exclusive foothold in our fields, and form a

sod in which the ordinary annuals are unable to flourish. Break up the sod after any number of years, and subdue the perennial grasses, and we shall have a crop of annuals the first season-Veronicas, Chenopodiums, Euphorbias, Portulacas, Ambrosias, Crab-grasses, Foxtails, Panicums, etc. Cease cultivation, and the Poas and Glycerias will immediately resume possession. Similarly, the pertinacity with which the common knot-grass seizes and maintains its position only along the hardest-beaten footpaths is notorious, while the greater plantain renders itself no less conspicuous growing alongside. Earth thrown out of cellars and wells is generally known to send up a ready crop of weeds, and, not unfrequently, of species previously unknown in that spot. In all these cases, after allowing for all known possibilities of the distribution of seeds by winds, birds, and waters, it still seems probable that germs must have previously existed in the soil.

Similar sudden appearances of new forms take place when a change is effected in the chemical nature of the soil. Illustrations are familiar to every agriculturist. How soon does a dressing of undecomposed muck, or peat, or sawdust develop a crop of acid-loving sorrel, and how readily is it again repressed by a dressing of some alkaline manure? Let the waters of a brine-well saturate a meadow, and how long before we witness the appearance of the maritime Scirpus and Triglochin, or some other saltloving plant whose germs, unless spontaneously developed, must have lain dormant at a greater or less depth?

Something of the same nature is witnessed on the disappearance of dominant species, whether through the agency of man or the processes of Nature. It is well known that the clearing of a piece of forest and the burning of the brush is almost always followed by the appearance of certain unwonted plants known as fire-weeds." In many

..

vital energy.

cases it would seem highly improbable that the seeds of such plants had recently been transported to such situations at the moment when the disappearing forest admits the introduction of the conditions essential to their growth. It can hardly be doubted that the seeds existed in the soil, ready to germinate whenever free sunlight, warmth, and atmospheric air should be permitted to rouse their latent Of the same nature is the recurrence of particular forest growths upon the same soil. Not unfrequently the second growth is of a very different nature from the first. In the "old fields" of Virginia and other Southern States, the soil, cleared originally of the deciduous forest, and then abandoned after years of continuous. cropping, sends up a growth of pines instead of deciduous trees. In some parts of Southern Ohio, as I have been informed, a forest of unmixed locust-trees follows the destruction of the ordinary mixed forest.

Mr. Marsh, in his learned work entitled "Man and Nature," has quoted from Dwight's "Travels" his account of the appearance of a fine growth of hickory on lands in Vermont which had been permitted to lie waste, when no such trees were known in the primitive forest within a distance of fifty miles. He quotes also Dr. Dwight's account of the appearance of a field of white pines, on suspension of cultivation, in the midst of a region where the native growth was exclusively of angiospermous trees. "The fact that these white pines covered the field exactly, so as to preserve both its extent and figure," says Dr. Dwight, “and that there were none in the neighborhood, are decisive proofs that cultivation brought up the seeds of a former forest within the limits of vegetation, and gave them an opportunity to germinate."

In this connection may be quoted a statement of Darwin, in "The Origin of Species," to the effect that in the midst