. Beginnings in agriculture. Agriculture. 56 AGRICULTURE At one time the north temperate lands were covered by a great glacier that reached across the continent to the Rocky Mountains. At certain points it extended as far south as Pennsylvania, and in some places was a thousand feet or more in height. As this vast ice sheet moved gradually southward, it ground the rocks into powder, wore away the sides of mountains, and rounded off the hill-tops. It carried much of the soil and rock with it, and as it gradually melted, deposited its load by the way. With the melting of so much ice, great strea
. Beginnings in agriculture. Agriculture. 56 AGRICULTURE At one time the north temperate lands were covered by a great glacier that reached across the continent to the Rocky Mountains. At certain points it extended as far south as Pennsylvania, and in some places was a thousand feet or more in height. As this vast ice sheet moved gradually southward, it ground the rocks into powder, wore away the sides of mountains, and rounded off the hill-tops. It carried much of the soil and rock with it, and as it gradually melted, deposited its load by the way. With the melting of so much ice, great streams were formed, which carried away much of the finer soil and left the coarser and heavier sand, gravel, and pebbles as sand^ banks or gravel banks. Perhaps near your home there are such banks, left by the glacier, remind- ing you that it once occupied your region or farm. There is now a glacier in Greenland covering an area more than ten times as great as that of New York State. It is slowly moving outward in all directions. From the ends that reach out into the sea icebergs break off, which, before they have melted, may float as far south as the path of ocean steamers. Similar glaciers are moving sea-ward from Alaska; and smaller ones are on many mountains. The work of plants. — The roots of growing plants creep into the crevices in the rocks, and there increase in size, force the cracks wider open, and break off fragments. Decaying plants and roots hold the moisture of rains, and so form an acid whhic slowly dissolves the rock that it Fig. 22. - A part of the edge of the Greenland glacier, showing its load of soil and Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Mann, Albert Russell, 1880-. New York, Macmillan company
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Keywords: ., bookcentury1900, bookdecade1910, bookpubl, booksubjectagriculture
