In the greater portion of the fields occupied by glacial waste the processes which lead to the introduction of organic matter into the earth have not gone far enough to set in effective work the great laboratory which has to operate in order to give fertile soil. The pebbles hinder the penetration of the roots as well as the movement of insects and other animals. There has not been time enough for the overturning of trees to bring about a certain admixture of vegetable matter with the soil--in a word, the process of soil-making, though the first condition, that of broken-up rock, has been accomplished, is as yet very incomplete. It needs, indeed, care in the introduction of organic matter for its completion. It is characteristic of glacial soils that they are indefinitely deep. This often is a disadvantageous feature, for the reason that the soil water may pass so far down into the earth that the roots are often deprived of the moisture which they need, and which in ordinary soils is retained near the surface by the hard underlayer. On the other hand, where the glacial waste is made up of pebbles formed from rocks of varied chemical composition, which contain a considerable share of lime, potash, soda, and other substances which are required by plants, the very large surface which they expose to decay provides the soil with a continuous enrichment. In a cubic foot of pebbly glacial earth we often find that the mass offers several hundred times as much surface to the action of decay as is afforded by the underlying solid bed rock from which a soil of immediate derivation has to win its mineral supply. Where the pebbly glacial waste is provided with a mixture of vegetable matter, the process of decay commonly goes forward with considerable rapidity. If the supply of such matter is large, such as may be produced by ploughing in barnyard manure or green crops, the nutritive value of the earth may be brought to a very high point. It is a familiar experience in regions where glacial soils exist that the earth beneath the swamps when drained is found to be extraordinarily well suited for farming purposes. On inspecting the pebbles from such places, we observe that they are remarkably decayed. Where the masses contain large quantities of feldspar, as is the case in the greater part of our granitic and other crystalline rocks, this material in its decomposition is converted into kaolin or feldspar clay, and gives the stones a peculiar white appearance, which marks the decomposition, and indicates the process by which a great variety of valuable soil ingredients are brought into a state where they may be available for plants.