some particles, now taking up others.  Other little streams join this one until they form a brook which increases in size and power as it descends the mountain side.  As it grows by the addition of other streams it picks up larger pieces, grinds them together, grinds at its banks and loads itself with rocks, pebbles, sand and clay.  As the stream reaches the lower part of the mountain where the slope is less steep, it is checked in its course and the larger stones and pebbles are dropped while the sand and finer particles are carried on and deposited on the bottom of some broad quiet river farther down, and when the river overflows its banks, are distributed over the neighboring meadows, giving them a new coating of soil and often adding to their fertility.  What a river does not leave along its course it carries out to sea to help build the sand bars and mud flats there.  The rain drops have now gotten back to the beach where they take up again the work of grinding the soil.

The work of moving water can be seen in almost any road or cultivated field during or just after a rain, and particularly on the hillsides, where often the soil is loosened and carried from higher to lower parts, making barren sand and clay banks of fertile hillsides and destroying the fertility of the bottom lands below.

We have already noticed the work of freezing water in splitting small and large fragments from the rocks.  Water moving over the surface of the earth in a solid form, or ice, was at an earlier period in the history of the earth one of the most powerful agencies in soil formation.  Away up in Greenland and on the northern border of this continent the temperature is so low that most if not all of the moisture that falls on the earth falls as snow.  This snow has piled up until it has become very deep and very heavy.  The great weight has packed the bottom of this great snow bank to ice.  On the mountains where the land was not level the masses of snow and ice, centuries ago, began to slide down the slopes and finally formed great rivers of solid water or moving ice.

The geologists tell us that at one time a great river of ice extended from the Arctic region as far south as central Pennsylvania and from New England to the Rocky Mountains.  This vast river was very deep and very heavy and into its under surface were frozen sand, pebbles, larger stones and even great rocks.  Thus it acted as a great rasp or file and did an immense amount of work grinding rocks and making soils.  It ground down mountains and carried great beds of soil from one place to another.  When this great ice river melted, it dropped its load of rocks and soils, and as a result we find in that region of the country great boulders and beds of sand and clay scattered over the land.