sides, but more especially on the east coast, while its central portion is nearly flat. On the whole the gradient decreases the further one gets into the interior, and the mass thus presents the form of a shield, with a surface corrugated by gentle, almost imperceptible, undulations, lying more or less north and south." The highest part is about 9,000 feet above the sea, and rather nearer the east coast than the west. How far this ice-sheet extends toward the north is not yet known; but Dr. Nansen remarks that its limit must lie beyond the 75th parallel, for so far along the west coast it sends huge glacier arms into the sea. Among these is Upernivik Glacier, which moves down at the rate of 99 feet in twenty-four hours. The thickness of this ice-sheet in the interior cannot, of course, be estimated; but no mountains rise above it, and those parts of it which come near the coast are considered to be from 2,000 to 3,000 feet thick.

On the western side of the country the edge of the inland ice is from 50 to 100 miles from the coast; but on the east coast large portions of it descend into the sea, and the peaks of nearly buried mountains (nunutaks) can be seen projecting above its surface, and only small tracts near the shore are free from ice. Both coasts are indented by fiords, the upper ends of which are generally barred by the ice-cliffs in which the huge glaciers terminate, and from which icebergs are being continually given off.

Nansen gives a section across South Greenland which shows the surface contour of the inland ice, but he makes no attempt to indicate the form of the ground beneath, though his observations afford some data for doing so. Thus the mountain peaks which rise through the ice near the east coast were all from 3,000 to 4,000 feet high, and between 40 and 50 miles inland he saw several nunutaks with elevations of over 6,000 feet. On the west coast the highest ground is often near the sea, and away from the inland ice, though in places this is parted by peaks and ridges from 2,000 to 3,000 feet high. The diagram, fig. 42, has been drawn in accordance with these indications, and will at any rate serve to give some idea of an ice-buried country. Fig. 43 is a portion of the inland ice descending to the sea as a glacier.

M

The interior of the island of Spitzbergen is also covered with a snow-field and ice-sheet from which huge glaciers descend into the sea; indeed, some parts of the coast consist almost entirely of the ice-cliffs in which the glaciers terminate. Mr. J. Lamont has described a glacier on the south-east coast which has a continuous front of ice 30 miles wide, and projects into the sea in three great semicircular divisions, the largest of them protruding for three or four miles beyond the real coast-line. The frontal icecliffs of this glacier vary from 20 to 100 feet in height, and from them masses of all sizes-up to that of a church—are continually breaking off and crashing into the sea. two outer lobes consist of smooth ice, but the inner one is so rough and jagged that, when seen dimly through the fog, "it resembles more than anything else a forest of pinetrees covered with snow."

The

The terminal position of some of these glaciers appears to vary; some have advanced and others retreated since they were first observed. Nordenskiold states that in Bell's Sound there was in 1858 a harbour, at the head of which was a strip of lowland, and beyond this a low but broad glacier. In 1860-61 the glacier advanced over the lowland, filled up the harbour, and extended far into the sea. "It now constitutes one of the largest glaciers in Spitzbergen, from which immense blocks of ice constantly fall down, so that not even a boat can venture in safety beneath its broken border." 1

Mr. Lamont says that many of the bergs which floated away from the ice-cliffs of Spitzbergen "were heavily charged with clay and stones," and that the sea for miles around is sometimes discoloured from the quantity of mud which is washed off this floating land-ice by the waves, and brought down by the torrents which elsewhere descend from the mountains.

Where mountains rise through an ice-sheet, lines of surface moraine are found, but when a whole region is buried in ice there can of course be no surface moraines, and the transport of detritus must be confined to the sole or base of the ice-sheet, and to the sub-current rivers. With

1 "Geol. Mag." Dec. 2, vol. iii. p. 18.

respect to the capacity of such ice-sheets for transport and erosion we know very little at present from actual observation, but as regards erosion, it may be safely asserted that if any part of a valley glacier exercises erosive power, those parts of an ice-sheet which move down buried valleys must have a more powerful erosive action.

It is believed that, at the period when the Swiss glaciers attained their greatest development and extension, North Britain and Scandinavia were covered by ice sheets which moved out in every direction from the main lines of watershed, which were then great gathering grounds of snow. The smoothened and rounded outlines of the lower hills in these countries, and the scratched and polished surfaces of the rocks on their sides, are generally attributed to the rasping and grinding action of these enormous masses of ice.

CHAPTER X.

MARINE AGENCIES.

ACTION of Waves. The upper surface of the sea is

kept in continual agitation by the force of the winds, which raise it into waves of all dimensions; these waves roll in upon every exposed coast-line throughout the world, and act as instruments of erosion and destruction. To estimate the power of sea-waves, they must be seen under the influence of a storm or gale of wind. Just as a brook in time of drought furnishes no measure of the work it does in time of flood, so the sea on a calm day gives no idea of the force with which storm waves can break on a rocky shore.

It has been ascertained that the average force of the breakers in winter time on the west coast of Scotland is equal to a pressure of 2,086 lbs. (nearly a ton) on every square foot of rock; during a storm it is greater. Mr. Stevenson found by experiments at the Bell Rock Lighthouse that the pressure was sometimes a ton and a half upon the square foot. and that at Skerryvore in the Atlantic it was doubly powerful, viz., about three tons to the square foot.

1

Such a force is evidently capable of dislodging and moving very large fragments of rock, especially if the blocks have been previously loosened by the action of rain and frost. Sir Arch. Geikie states that on the coast of the Pentland Firth blocks from 7 to 13 tons in weight had been quarried out of the cliffs at a height of 70 feet above the sea; the waves must have risen to that height, and still have been able to bring down these immense frag

1 64 Scenery and Geology of Scotland,” p. 61.