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He should see that his work brings two risks; he may impoverish the accumulation of detrital material by taking out the plant food more rapidly than it is prepared for use. This injurious result may be at any time reparable by a proper use of manures. Not so, however, with the other form of destruction, which results in the actual removal of the soil materials.
From all of which we see that the Eastern hemisphere's crescent hollow of which, I take it, the Mediterranean, Black, and Caspian Sea depressions are the remains has been gradually filled in, by the elevation of the sea's bottom, and the extension of deltas from the detrital matter brought from the high interior of the continents by the rivers, or by the combined action of the two.
The effect of allowing the water to penetrate is not only to diminish the superficial wearing, but to maintain the process of subsoil and bed-rock decay by which the detrital covering is naturally renewed.
The people used ladders, but they neglected to collar or brace the mouth, and the untimbered pit-sides often fell in; hence fatal accidents, attributed to the 'earth-spirits. They held gold to be a capricious elf, and when a rich vein suddenly ran barren they cried out, 'There! he is off! Here the natives collect dust by laborious washings of detrital sand.
Not only does the land life maintain itself on the soil, and give much to the sea, but it serves in various ways to protect this detrital coating from too rapid destruction, and to improve its quality. To see the nature of this work we should visit a region where primeval forests still lie upon the slopes of a hilly region.
These accumulations of rocky fragments and detrital matter are left at the termination of the glacier, where it melts in a confused heap called the "terminal moraine," which is unstratified, because all the blocks, large and small, as well as the sand and the finest mud, are carried to equal distances and quietly deposited in a confused mass without being subjected to the sorting power of running water, which would convey the finer materials farther than the coarser ones, and would produce, as the strength of the current varied from time to time in the same place, a stratified arrangement.
Georgian Bay, 170 miles long and 70 broad, forms the northeast portion, and lies within British jurisdiction. Saginaw, a deep and wide-mouthed bay, is the principal indentation on the western coast. The rim of this lake is composed mostly of detrital rocks, which are rarely exposed. In the northern portion of the lake, the trap-rocks on the Canada side intersect the coast.
It is now necessary for us to take up the phenomena of soils in a consecutive manner. The study of any considerable river basin enables us to trace the more important steps which lead to the destructure and renovation of the earth's detrital coating.
In almost every large area the process of erosion naturally leaves quantities of rock, either in the form of detached columns or as detrital accumulations deposited on steep slopes. These features are of relatively slow formation, and it is often possible to determine that they have been in their positions for a time which is to be measured by thousands of years.
They may be formed in what are called dead seas, in which case the detrital materials are commonly small in amount, for the reason that the inflowing streams are inconsiderable; in such basins there is normally a large share of saline materials, which are laid down by the evaporation of the water.
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