PRACTICAL ARBORICULTURE 149 



EROSION. 



Nothing remains stationary in nature. Changes are constantly occurring. 

 Worlds move constantly in their orbits through the heavens. The earth ever 

 continues to tear down the wondrous monuments of past epochs, and to erect 

 new geological formations. One great force of nature upheaves the land at 

 one place, depressing it elsewhere, and in these operations mountain chains 

 are elevated, volcanoes, earthquakes, seismic exhibitions are but partial effects 

 of this enormous force. Another element is at work tearing down the moun- 

 tains, leveling the hills and sweeping clown to lower levels the looser portions 

 of the surface, from the mountain plain and valley. This power is erosion. 



Alternate freezing and thawing of the water on the higher mountains 

 rend asunder the granite rocks, and hurl them far down the valleys ; torrents 

 of water roll these fragments along the mountain streams, grinding them 

 into powder, which is borne by the currents to the ocean. This same power, 

 flowing water, washes the soil from ten thousand farms, and mingles it with 

 the debris from granite peaks, strewing it about the deltas of all great rivers. 



It is this erosion, by flowing waters, that so constantly channels out the 

 farms on rolling lands, and removes the richest portions of fertile fields of 

 every thriftless farmer. The tendency to clear away all forest growths from 

 every steep hillside, to bare the banks of every stream, for the purpose of 

 obtaining a few crops while the land is new and the soil fertile, is destructive 

 of farm lands and a very injurious practice. 



Such lands can be cultivated but a few years, when they are abandoned 

 as worn out soils. 



The roots of trees hold the soil from washing while in forest, but as the 

 trees are removed the roots decay, and the ground being loosened by the 

 plow, is soon washed into the streams. 



While such lands remain covered with trees, the annual deposit of leaves 

 continues to enrich the soil, and, gradually carried to the lower fields, renew 

 their fertility, but with removal of these hillside forests the torrents come 

 with unimpeded velocity, to destroy the lower fields as well as those upon 

 the hillside. 



The Ohio Valley is but one instance where half a century ago there 

 existed the richest land on the continent, but erosion has left the clay and 

 rocks, with fields unfertile and difficult to till. 



Prior to the Civil War period the Ohio and Mississippi rivers were the 

 great channels of commerce between the North and the South. Many 

 thousands of tons of farm produce were annually shipped by flat boats to the 



