prodigious amount of fine earth up into the open air. With this material it builds hills sometimes 60 feet high and visible for a distance of several miles; likewise tunnels and chambers, which it plasters all over the stems and branches of trees, often so continuously that hardly any bark can be seen. The fine soil thus exposed is liable to be blown away by the wind or washed off by the fierce tropical rains.

Although, therefore, the layer of vegetable soil which covers the land appears to be a permanent protection, it does not really prevent a large amount of material from being removed even from grassy ground. It forms the record of the slow and almost imperceptible geological changes that affect the regions where it accumulates, the quiet fall of rain, the gradual rotting away of the upper part of the rock underneath, the growth and decay of a long succession of generations of plants, the ceaseless labours of the earth-worm, the scarcely appreciable removal of material from the surface by the action of rain and wind, and the equally insensible descent of the crumbling subsoil farther and farther into the solid stone below. Having learnt how all this is told by the soil beneath our feet, we should be ready to recognise in the soil of former ages a similar chronicle of quiet atmospheric disintegration.

Talus. Besides soil and subsoil, there are other forms in which decomposed rock accumulates on the surface of the land. Where a large mass of bare rock rises up as a steep bank or cliff, it is liable to constant degradation, and the materials detached from its surface accumulate down the slopes, forming what is known as a Talus (Fig. 4). In mountainous or hilly regions, where rocky precipices rise high into the air, there gather at their feet and down their clefts long trails or screes of loose blocks split off from them by the weather. Such slopes, especially where they are not too steep, and where the rubbish that forms them is not too

FIG. 4. Talus-slopes at the foot of a line of cliffs.

coarse, may be more or less covered with vegetation, which in some measure arrests the descent of the debris. But from time to time, during heavy rains, deep gullies are torn out of them by rapidly formed torrents, which sweep down their materials to lower levels (Fig. 10). The sections laid bare

7

6

5

4

3

2

A

in these gullies show that the rubbish is arranged in more or less distinct layers which lie generally parallel with the surface of the slope; in other words, it is rudely stratified, and its layers or strata are inclined at the angle

FIG. 5.-Section of rain of the declivity which seldom exceeds

wash or brick-earth.

7. Vegetable soil. 6. 35°

Brick-earth. 5. White

Rain-wash, Brick-earth.-On

sand. 4. Brick-earth. more gentle slopes, even where no bare 3. White sand. 2. rock projects into the air, the fall of rain

mixed often with angular fragments of still undecomposed rock, and not infrequently forming a kind of brick-earth (Fig. 5). Deposits of this nature are still gathering now, though their lower portions may be of great antiquity. In the south-east of England, for instance, the brick-earths contain the bones of animals that have long since passed away.

Dust. By the action of wind, above referred to, a vast amount of fine dust and sand is carried up into the air and strewn far and wide over the land. In dry countries, such as large tracts of Central Asia, the air is often thick with a fine yellow dust which may entirely obscure the sun at mid-day, and which settles over everything. After many centuries, a thick deposit is thus accumulated on the surface of the land. Some of the ancient cities of the Old World, Nineveh and Babylon for example, after being long abandoned by man, have gradually been buried under the fine soil drifted over them by the wind and intercepted and protected by the weeds that grew up over the ruins. Even in regions where there is a large annual rainfall, seasons of drought occur, during which there may be a considerable drifting of the finer particles of soil by the wind. We probably hardly realise how much the soil is in some regions removed and in others heightened from this cause.

Sand-dunes. Some of the most striking and familiar examples of the accumulation of loose deposits by the wind are those to which the name of Dunes is given. On sandy shores, exposed to winds that blow landwards, the sand is dried and then carried away from the beach, gathering into long mounds or ridges which run parallel to the coast-line. These ridges are often 50 or 60 feet, sometimes even more than 250 feet high, with deep troughs and irregular circular hollows between them, and they occasionally form a strip several miles broad, bordering the sea. The particles of sand are driven inland by the wind, and the dunes gradually bury fields, roads, and villages, unless their progress is arrested by the growth of vegetation over their shifting surfaces. On many parts of the west coast of Europe, the dunes are marching into the interior at the rate of 20 feet in a year. Hence large tracts of land have within historic

times been entirely lost under them. In the north of Scotland, for example, an ancient and extensive barony, so noted for its fertility that it was called "the granary of Moray," was devastated about the middle of the seventeenth century by the moving sands, which now rise in barren ridges more than 100 feet above the site of the buried land. In the interior of continents also, where with great dryness of climate there is a continual disintegration of the surface of rocks, wide wastes of sand accumulate, as in the deserts of Lybia and Arabia and in the heart of Australia.

There can be no doubt, however, that though in the layer of vegetable soil, in the heaps of rubbish that gather on slopes and at the base of rocky banks and precipices, and in the widespread drifting of dust and sand over the land by the action of the wind, we have evidence that much of the material arising from the general decay of the surface of the land accumulates under various forms upon that surface, nevertheless its stay there is not permanent. Wind and rain are continually removing it, sometimes in vast quantities, into the sea. Every brook, made muddy by heavy rain, is an example of this transport, for the mud that discolours the water is simply the finer portions of the soil washed off by rain. When we reflect upon the multitude of streams, large and small, in all parts of the globe, and consider that they are all busy carrying their freights of mud to the sea, we can in some measure appreciate how great must be the total annual amount of material so removed. What becomes of this material will form the subject of the succeeding chapters.

Summary. The first lesson to be learnt from an examination of the surface of the land is, that everywhere decay is in progress upon it. Wherever the solid rock rises into the air, it breaks up and crumbles away under the various influences combined in the process of Weathering. The wasted materials caused by this universal disintegration partly accumulate where they are formed, and make soil. But in large measure, also, they are blown away by wind and washed off by rain. Even where they appear to be securely protected by a covering of vegetation, the common earthworm brings the fine parts of them up to the surface, where they come within reach of rain and wind, so that on tracts permanently grassed over, there may be a continuous and