and become part of its mass. The coast-ice is thus charged with a load of stones and boulders both on its upper and lower surfaces, just in the same way as glacier-ice is, only the quantity of débris is probably greater.

As the thaw proceeds in summer time, this ice-foot is broken up by the waves, and large masses are driven on to the shore during storms, crushing and grinding the rocks over which they are pushed; other portions are separated from the coast and floated out to sea, forming great rafts or floes, each with its load of rock débris.

Even in calmer weather it is clear that coast-ice, having numerous fragments of rock fixed in it, and being borne backwards and forwards by the tide, must exercise an enormous grinding and grooving action. Both the stones themselves and the surfaces over which they are moved will be scratched and abraded, and much mud will be produced by the process. It may be observed, also, that a stone fixed in the ice-foot, and scratched along one side by contact with the rock below, may be dropped when the ice begins to thaw, and afterwards ground along its other sides by the stones still fixed in the ice above, so that it may eventually bear scratches all over it, as is the case with so many stones in our Boulder clays.

Speaking of ice-action on the coasts of Grinnell Land, part of North Greenland, Messrs. Fielden and De Rance make the following observations: "Sea-ice driven on shore by gales, or moving up and down with the tides, is a very potent factor in glaciating rocks and pebbles. Along the shores of the Polar basin this process of glaciating was seen in progress by one of us; and he records in his Journal' that at the south end of a small island in Blackcliff Bay (lat. 82° 30 N.), the bottom of the ice hummocks, some 8 to 15 feet thick, were studded with hard limestone pebbles, which were rounded and scratched as distinctly as others taken from moraines; when extracted from the ice, only the exposed surfaces, as a rule, were glaciated. As the tide recedes the hummocks do not always arrive at a position of rest without some disturbances of the subjacent material, particularly on a shelving

1 "Quart. Journ. Geol. Soc.," vol. xxxiv. p. 566.

shore, and the sliding of the hummock to a lower level, and the sound following on the grating together of the pebbles beneath may be noted. In many places where gaps occurred in the lines of ancient sea-terraces, the basement rock, as well as some of the pebbles in the terraces, were found to be glaciated, and there can be no doubt that this is due to the action of shore-ice, the condition of the terraces precluding the idea that it might have been the result of glacier action."

An illustration of the action of such ice on a shelving shore in a much lower latitude is mentioned by Dr. Forchhammer,' who states that during a hard frost in February, 1844, sheets of ice were formed in the Sound between Sweden and Zealand, and some of these were driven by a storm into the Bay of Täarbejik, and forced up on the beach, forming a mound more than 16 feet high. When he visited the spot next day, he saw "ridges of ice, sand, and pebbles, not only on the shore, but extending far out into the bottom of the sea, showing how greatly its bed had been changed, and how easily, where it is composed of rock, it may be furrowed and streaked by stones firmly fixed in the moving ice."

To the action of such masses, but still more to that of ground-ice which forms on shallow bottoms, and contains stones frozen into its under surface, Professor Forchhammer attributes the striation of the rocky surfaces round the shores of the Baltic.

When to the ordinary action of tides and winds is added the impact of some of the large masses of ice, which are set loose from the Arctic regions in summer time, and are often driven on to the more southern coasts, still greater results are produced. The action of this pack-ice on a shelving shore is thus described by Professor Milne: 2"When we reflect upon the immense mass in one of these moving fields of ice, we can hardly conceive the energy that is stored within it. Everything has to give way before it; and the coast-ice, with its set of gravers firmly bedded in its base, is pushed high and dry, sometimes as much as

1

2 44

Bull. Soc. Géol. de France, 1847," tom iv. p. 1182. 'Geological Magazine," Dec. 2, vol. iii. p. 405.

100 yards back from high-water mark. It is in this way, by the coming-in of the northern pack, the rise and fall of the tide, and other causes, that the land-ice is driven ashore, and many of the scratches and grooves so common round the coast of Newfoundland have been made."

Sir George Nares observed that in some places on the coast of Grinnell Land huge floe-bergs and ice-blocks had been forced up on the inclined shore, until a rampart-like barrier of solid ice-blocks was accumulated, measuring about 200 yards in breadth, and rising 50 feet high.'

The impact of this floe-ice seems also to have a rounding and moulding effect upon such islands and prominences of rock as are exposed to its force, producing forms which, on a large scale, resemble the roches-moutonnées formed by glaciers. Professor Milne instances a small islet called Funk Island, near Newfoundland, which is situated directly in the course of the ice-floes coming southward from Baffin's Bay and Labrador. "The northern end of this island, which has every year to face the pressure of the vast fields of ice which are borne down upon it, is visibly worn down, and covered with erratic boulders, whilst the opposite extremity is a low but abrupt cliff."

He argues, therefore, that much of the stratching and modelling which has hitherto been referred to the action of enormous glaciers, may have been produced by the agency of coast-ice and floe-ice acting on the surface of the country during its last slow emergence from the sea.

The part taken by these ice-floes in transporting and depositing material will be described on a future page.

1 "Voyage to the Polar Sea," vol. i. p. 276.

AT

SECTION II. (continued).

B. Processes of Reconstruction.

CHAPTER XI.

T the commencement of Section II. it was stated that in considering the agencies concerned in the continual detrition and renewal of the earth's surface, we should first describe their destructive and dispersive effects, reserving all mention of their reconstructive effects to a future section. Accordingly we now proceed to give some account of the manner in which new deposits are formed out of the materials obtained by the several agencies already described, and to indicate the nature of the formations thus produced. These may be divided into four classes, according to the conditions under which they have been accumulated, each except the second being subdivided into three groups according as they owe their formation to mechanical agencies, to chemical action, or the growth of organic matter. The deposits formed by rivers and glaciers, however, are all the result of mechanical action.

This classification is set out in the following table :Rain, frost, and wind Mechanical. Springs and percolating

Terrestrial

water

Worms and plants

Rivers

Fluviatile

Chemical.
Organic.

Mechanical.

Glaciers

Subsiding sediment.

Evaporation of water.

Mechanical.

Chemical.

Organic.

1. Soil and Rain-wash.-It was shown in Chapter VI. that the heat of the sun, the fall of rain, and the freezing of water exercise a powerful effect upon the surface of all rocks at or near the surface of the earth, and lead to their gradual decay and disintegration.

In temperate and humid climates rain is by far the most potent of these agencies; acting in the first place chemically by means of the acids and oxygen which it contains, it decomposes and dissolves some of the constituents of the rocks exposed to its influence, and so loosens the coherence of their constituent particles that they are rendered soft and crumbling to a greater or less depth from the surface. This rotten and decomposed portion of the rock is then subjected to still further disintegration by the mechanical action of the falling drops of rain, and the lighter particles are eventually washed away by the rills into which the rain-drops collect, while the residue remains to form the soil of the district.

The various kinds of soil which mantle the earth's surface, and conceal the underlying rock or subsoil, have been primarily produced in this way, the formative action being assisted, as we shall presently see, by the agency of plants and earth-worms. The nature of the soil, therefore, depends largely upon the character of the rock beneath, and is heavy or light according as argillaceous or arenaceous matter preponderates in the rock from which it has been formed. Its quantity, too, depends partly on the kind of rock acted upon, its capacity or incapacity of resisting disintegrating agents, and partly upon the contour and slope of the ground.

It has been ascertained that the soil has everywhere a