the ground with rocks and stones in those sections, as he had in New York and New England.  South of the line that runs irregularly through middle New Jersey, Pennsylvania, Ohio, Indiana, Illinois, Iowa, and so on to the Rockies, he will find few loose stones scattered over the soil, no detached boulders sitting upon the surface, no hills or mounds of gravel and sand, no clay banks packed full of rounded stones, little and big, no rocky floors under the soil which look as if they had been dressed down by a huge but dulled and nicked jack-plane.  The reason is that the line I have indicated marks the limit of the old ice-sheet which more than a hundred thousand years ago covered all the northern part of the continent to a depth of from two to four thousand feet, and was the chief instrument in rounding off mountain-tops, scattering rock-fragments, little and big, over our landscapes, grinding down and breaking off the protruding rock strata, building up our banks of mingled clay and stone, changing the courses of streams and rivers, deepening and widening our valleys, transplanting boulders of one formation for hundreds of miles, and dropping them upon the surface of another formation.  When it began to melt and retreat, it was the chief agent in building up our river terraces, and our long, low, rounded hills of sand and gravel and clay, called kames and drumlins.  In many of our valleys its flowing waters left long, low ridges, gentle in outline, made up entirely of sand and gravel, or of clay.  In other places it left moraines made up of earth, gravel, and rock-fragments that make a very rough streak through the farmer’s land.  All those high, level terraces along the Hudson, such as that upon which West Point stands, were the work of the old ice-sheet that once filled the river valley.  The melting ice was also the chief agent in building up the enormous clay-banks that are found along the shores of the Hudson.  The clay formed in very still waters, the sand and gravel in more active waters.

This great ice-sheet not only covered our northern farms with rocks and stones, and packed the soil with rounded boulders, but it also carried away much of the rock decay that goes to the making of the soil, so that the soil is of greater depth in the non-glaciated than in the glaciated areas of the country.  The New-Englander or New-Yorker in traveling in the Southern States may note the enormous depth of soil as revealed by the water-courses or railroad cuts.  The ice-sheet was a huge mill that ground up the rocks in the North probably as fast or faster than the rains and the rank vegetation reduced them in the South, but the floods of water which it finally let loose carried a great deal of the rock-waste into the sea.