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Nitrogen is both the most abundant agriculturally and the most expensive commercially of all the elements of plant food; and yet there is a method by which it can be secured not only without money but with profit in the process. The percentage of nitrogen in normal soils decreases with depth, so that subsoils are almost devoid of nitrogen.
The preglacial subsoils were residual clays and sands, composed of the insoluble elements of the country rock of the locality, with some minglings of its soluble parts still undissolved. The glacial subsoils are made of rocks of many kinds, still undecayed and largely ground to powder.
OXIDATION. Rocks containing compounds of iron weather to reddish crusts, and the seams of these rocks are often lined with rusty films. Oxygen and water have here united with the iron, forming hydrated iron oxide. The effects of oxidation may be seen in the alteration of many kinds of rocks and in red and yellow colors of soils and subsoils.
The share which worms have taken in the formation of the layer of vegetable mould, which covers the whole surface of the land in every moderately humid country, is the subject of the present volume. This mould is generally of a blackish colour and a few inches in thickness. In different districts it differs but little in appearance, although it may rest on various subsoils.
To these soils and subsoils a large part of the wealth and prosperity of the glaciated regions of our country must be attributed. The ice invasions have also added very largely to the water power of the country.
It leaches soils and subsoils of their lime and other soluble minerals upon which plants depend for their food. It takes away the soluble cements of rocks; it widens fissures and joints and opens winding passages along the bedding planes; it may even remove whole beds of soluble rocks, such as rock salt, limestone, or gypsum.
Thousands of details about drainage, ventilation, shoring, architectural practice, lighting, subsoils, specifications, iron and steel construction, under-pinning, the properties of building materials, strains, thrusts, water-supply; thousands of details about his designs the designs in his 'testimonies of study, the design for his Thesis, and the designs produced during the examination itself all these peopled his brain; but they were in order; they were under control; they were his slaves.
We must remember that Karst regions are rare, and striking as is the work of their subterranean streams, it is far less important than the work done by the sheets of underground water slowly seeping through all subsoils and porous rocks in other regions.
Of course, a number of popular causes, such as bad drainage, the drinking of water from shallow surface wells, damp subsoils under the houses, and especially that peculiarly widespread and firmly held article of belief that new settlements, where large areas of prairie sod were being freshly upturned by the plough, were peculiarly liable to the attack and spread of malaria, had to go by the board, with this important reservation, however, that almost every one of these alleged causes either implied or was pretty safe to be associated with pools or swamps of stagnant water in the neighborhood, which would furnish breeding-spots for the mosquitoes.
The geologist's theory, combined with the knowledge that the noble metal is 'chiefly found among palæozoic rocks of a quartzose type, is practically valuable on the Gold Coast. Every mound or hillock of red clay contains one or more quartz-reefs, generally outcropping, but sometimes buried in the subsoils. They can always be struck by a cross-cut trending east-west.
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