There are even other differences than these, and one who is familiar with a region is often puzzled to explain them; but they are all due to the glacier or to the water furnished by its melting, and a careful study by a student of the subject of Glacial Geology will serve to explain them. Each place has had peculiar conditions and it would be necessary to study each place much more carefully than has been done here in order to explain all the differences.
Not only is agriculture influenced greatly by the differences in the soil from place to place, but also by the very fact that they are glacial soils. Being made up of partly ground-up rock fragments the soils are often stony and difficult to till. Unlike the soil of rock decay, the particles of which the glacial soil is made have been derived by mechanical grinding, not by chemical decay and disintegration. There has been less leaching out of the soluble compounds which make plant foods. These are stored up in the rock fragments ready for use when decay causes the proper changes to produce the soluble compounds which plants require.
Fig. 34. Hummocky moraine hills in the background and a level gravel plain—an ancient glacial-stream flood-plain—in foreground.
Slowly the glacial soils are decaying, and, as they do so, are furnishing plant-food to the water which the roots greedily draw in. So the glacial soil is not a mere store house of plant-food, but a manufactory of it as well, and glacial soils are therefore "strong" and last for a long time. That decay is going on, especially near the surface, may often be seen in a cut in the soil, where the natural blue color of the drift is seen below, while near the surface the soil is rusted yellow by the decay of certain minerals which contain iron.
Few materials on the earth are more important than the soil; it acts as the intermediary between man and the earth. The rocks have some substances locked up in them which animals need; by decay, or by being ground up, the rocks crumble so that plants may send roots into them and extract the substances needed by animals. Gifted with this wonderful power the plants grow and furnish food to animals, some of which is plant-food obtained from the rocks; and so the animals of the land, and man himself, secure a large part of their food from the rocks. It is then worth the while to stop for a moment and think and study about this, one of the most marvelous of the many wonderful adjustments of Nature, but so common that most persons live and die without even giving it more than a passing thought.
LEAFLET IX.
A HANDFUL OF SOIL: WHAT IT DOES.[11]
By L. A. CLINTON.
