The people in Pennsylvania desired the salt which was obtained in New York, but it cost $2.50 a bushel to carry salt three hundred miles. Citizens of Philadelphia would have purchased flour which was raised about the sources of the Susquehanna River had it not cost $1.50 a barrel to carry it to Philadelphia. Hundreds of families were weekly moving westward into the new country across the Alleghany Mountains; they could not afford to take their household goods with them. The freight charges from New York to Buffalo were $120 a ton; from Philadelphia to Pittsburg, $125. Something new in the line of transportation was needed; some way by which freight could be carried at less expense. Private companies were building new toll roads--but these did not accomplish the purpose. Different States expended money in improving the highways, and still the expense of transportation was enormous. The national Government also took part in the work and constructed a highway from Cumberland, Maryland, to Wheeling, on the Ohio River--but this was merely a single road over the mountains, and freight charges were as high as ever. What could be done? Of course the roads everywhere must be improved and new ones built--all of which would take many years. But was there not some way to avoid carrying so much freight in wagons drawn by horses? Wherever there were rivers these could be used. Was it possible to make rivers, or at least to make water-ways, upon which boats might be used? The people of the United States began to talk of canals, and soon enthusiasm for canal building became universal. What is a canal? It is a trench cut in the ground, filled with water deep enough for a well-laden boat, and wide enough for boats to pass each other. On one bank is a path, called the towpath, upon which horses or mules travel, pulling a canal boat behind them by means of a long rope. In most canals it is found necessary to lift the boats over higher land or up to a higher level. This is done by locks, which are built where the two levels of the canal come together. These locks are shut off from each part of the canal by gates. When the lower gates are shut and the upper gates open, water is let into the lock from the upper canal until on a level with it. Then a canal boat from the upper canal enters the lock. The upper gates are closed, the lower gates opened, and the water runs out of the lock. The boat, remaining on top of the water, sinks to the lower level and is ready to proceed on its course. In traveling the other way the process is turned about. The boat enters the lock and rises with the water which is let in from above until it is on the upper level.