CHAPTER XIX.

THE REIGN OF ICE.

THEN the continent of North America, which had been growing through unnumbered ages by continual annexations of land wrested from the dominion of the sea, had finally attained the dimensions and outline destined to endure through the human era-when the great mountain axes had been uplifted, and the broad river streams were rolling the drainage of the valleys and hillslopes to the sea-when the horse and the camel, the elephant, the bear, and other quadrupeds which were to characterize the epoch of man, had assumed their stations on the land-when the atmosphere was populated by birds and insects which were destined in a coming age to be startled by the presence of a dominant intelligence-when the beech, the tulip-tree, the linden, and the buttonwood had taken their places on the jungle's margin and the highland slope, and the sorrowing willow had begun to weep above the flowing waters of the sedge-bordered streamwhen the whole face of Nature seemed fitted and expectant of the crowning work of creation, what should prevent the divine Artificer from summoning man upon the scene to begin the labor of his earthly life? To a finite intelligence the preparation was complete. To the eye of Omniscience one more revolution was needed. The coming man must tarry without the doors of the temple of life through yet another geological æon.

To this time the evolution of the continent had proceeded by elevations and subsidences of the regions lying in

the middle latitudes, the resultant of which movements was the establishment of a vast area of dry land extending over all that portion of North America covered by the temperate zone. The northern regions were still the bed of a vast circumpolar ocean. Now, in turn, the high northern latitudes experience an unwonted uplift. Arctic lands raise high their dripping heads above the temperate waters of the polar zone. The climate of the whole northern hemisphere feels the change. No moving currents can now bear torrid warmth to the frozen sea, and return the colder waters to the equatorial zone. The stable land bears sternly the vicissitudes of the clime, smiling coldly in the slanting rays of a summer's sun, and gloaming darkly beneath the auroral shimmering of arctic midnight. The accumulated cold of years binds all the northern latitudes in indissoluble bonds of ice. The northern blast bears frost along the vales which had never felt its power. The limpid streams grow torpid, and then rest in a long hibernal sleep. The verdure of forest and plain, touched by the first breath of winter, shrinks away, and the sere and blackened leaf hangs where there had been perennial green. The ponderous tread of the mastodon turns from the withered meadow to the frozen jungle, and the shivering tapir yields himself a victim to the strange rigors of the climate. The snows of many winters are gathered on the slopes of northern America, and the summer's sun suffices but to change them to a bed of porous ice. Glaciers brood over all the land, and Alpine desolation reigns without a rival over half the continent. Such was the fate of the fair vales which we thought just ready for the occupancy of the hu

man race.

The marks of this stupendous glacier are still visible. As in the glaciers of the Alps, the expansion produced by a summer's warmth would tend to create a motion in the

margins of the ice-field.

The northern limit was chained

by eternal frost to its rocky bed. The southern only was free to move, and the whole expansion would be developed along the southern border. The sliding movement of incalculable tons of ice would plow the soil beneath. Rockfragments, pebbles, and gravel, frozen in the under surface, were carried forward by the moving mass, while the underlying rocky surfaces were ground away, or polished, or scored in parallel furrows by the irresistible agency of the glacier (Fig. 80). These phenomena are noticeable all over the Northern States wherever the "bed rock" is exposed to view. The bold shore of the north side of Lake Superior has been extensively carved and modified by this resistless action. At Marquette, upon the south shore, are some striking and instructive illustrations. A low dome of metamorphic talcoze schist rises a few feet above the surface of the water at the shore, nearly in front of the Jackson house, which bears the imperishable tracery of its conflict with the continental glacier. The whole surface is smoothed as with a carpenter's plane and sand-paper. The undulations in the surface are scoured as neatly as the level and more prominent portions. Rising from beneath the water on the northern side can be seen numerous grooves and scratches, which glide up the smoothed northern slope, and extend continuously across the summit to the southern side. There are two principal sets of these striæ. One of them extends nearly north and south, the other northeast and southwest. Near this place, and close by the main street as it passes out of town, is an isolated outlying mass of the same kind of rock, which has been left standing out boldly after the destructive agencies that have passed over the surface had plowed away all the surrounding portions of the formation. This stubborn mass stands like a sullen bulwark, defying the most desperate attacks of ice, or

storm, or flood. But its lowering brow shows the deep scars of many a fierce conflict. The attacks have evidently proceeded from the north. On this side the perpendicular walls are smoothed and scored in precisely the same manner as the dome-shaped mass to which I have just alluded. The southern side retains, like the other mass, many of the angularities produced by the original fractures of the formation. Similar features are things of every-day observation, but people never suspect what mighty and what extraordinary agencies have been employed in producing them. All our low rocky hills and bluffs are similarly pared off upon their summits and northern exposures, while their southern aspects are more rugged. The great glacier has passed over them, striking them from the north, and grinding down their northerly projections and angularities. These phenomena have been especially studied. and illustrated in New England by the lamented Dr. Hitchcock. On the western end of Lake Erie, at Stony Point, the surface of the Corniferous limestone lies two or three feet above the level of the water. Upon this have been deposited four or five feet of gravel and soil. On the immediate shore, the storm-waves have easily washed off the overlying beds, and left acres of the limestone completely exposed to view. What do we find to be the character of this original surface? Level and smooth as a floorplaned down by the energy of the omnipresent glacierbut marked, besides, by some deep furrows, which extend from edge to edge of the uncovered table in lines as straight and strictly parallel as if marked by the "gauge" of some Titanic stone-worker. One set of the furrows, in particular, arrests the attention, since the visitor can not fail to recognize their resemblance to the deep ruts produced by a loaded wagon moving over a soft and clayey surface (Fig. 81).

K