How Ice Has Made Soil

Once the northern part of North America was covered with a great sheet of ice, reaching as far south as Cape Cod, northern Pennsylvania, Ohio and westward to the Rockies. Geologists tell us that this immense glacier must have been several hundreds, and in some places several thousands of feet thick. It slowly bore down from the north, moving only a few inches to a few feet an hour, scraping the surface of the earth and carrying great quantities of rocks, stones and soil to the southward. According to some authorities certain parts of the glacier must have exerted a pressure of at least two hundred thousand pounds per square inch upon parts of the surface over which it passed. The bottom of the ice sheet became studded with huge boulders, which acted like teeth, tearing and grinding the rocks over which the ponderous mass passed. Some of these boulders, scratched and worn, may be still seen in the hillside pastures of New England and other parts of the glaciated region.

Some exposed ledges of rock still show the deep grooves that were cut in them by these boulder teeth. When the ice melted a mass of soil material was dropped, perhaps many hundreds of miles away from the place where it was picked up. Rocks that could have come only from the mouth of Lake Huron are found in the drift or glacial soils in Ohio. Rocks from Ontario are found as far south as Kentucky. Great masses of ice were stranded here and there over the land. The streams of water resulting from the melting of the ice still further mixed the rocks, and the soils that the glacier had ground from the rocks. The result of this ice sheet is the endless variety of soils that are found in the North.

Most of the soils of that part of the northern United States that was covered by the great glacier were made by this agency. They are technically known as "drift" soils. Where parts of the ice sheet settled and melted away there were formed "morains" or "drumlins," the long, rounded knolls so common in north-eastern United States. Since the time when this ice sheet covered our land, moving water has still further shifted and mixed soils, rounded the knolls and deepened the gullies. But most of the great variety of soil and diversity of contour in this region is due to the scouring, crushing, molding, transporting and distributing power of the great glacier. Small glaciers, performing exactly the same work, may be seen to-day in the Alps, Alaska, and other frigid regions.