If a region is perfectly level, only a ditch and water are needed. But lands are not often level for more than short distances; hence a canal consists commonly of a series of levels at different heights. Of course the boats must be passed from one level to another by some means. If they are small, they can be dragged up or down between two levels; but this method will not serve for large boats carrying many tons of coal, lumber, salt, or bricks, hence locks are generally used. A lock is a short section of a canal, long enough for the boats used, and having walls rising from the bottom of the lower level to the top of the upper one. There are big gates at each end. If a boat is to ascend, it runs into the lock on the lower level and the lower gates are closed. A small gate in the large upper gate is then opened and the water runs in from above, slowly raising the water in the lock and with it the boat. When the water in the lock is even with the water in the upper level, the big upper gates are swung open and the boat goes on its way. In a similar manner boats go down from higher to lower sections of the canal. Locks have been used in Italy and in Holland for more than four hundred years. On April 15, 1817, the legislature passed the law for the construction of the long ditch, and the first spade was set into the earth by Judge John Richardson at Rome, New York, on July 4 of the same year. This was forty-one years after the Declaration of Independence, and it is plain that the country had grown much in wealth and numbers when a single state could start out to build a water way three hundred miles long. After the first spadeful of soil had been lifted, the citizens and the laborers eagerly seized the shovels, and thus everybody had a small share in beginning the great work. Guns were fired and there was much rejoicing. [Illustration: FIG. 14. ERIE CANAL, LOOKING EAST FROM GENESEE STREET BRIDGE, UTICA] The men who took the contracts for digging short sections of the canal were mainly farmers who had gained good properties and who were living along the line. In those days, if any one had visited the men at work, he would not have seen crowds of foreign laborers living in huts, but men born and reared in the country round about. It was little more than twenty years since the Genesee road had been built through central New York, and there was still much forest. The trees grew rank and strong, and it was no light task to cut through the tangled network of roots that lay below the surface. First the trees were cut down, making a lane sixty feet wide, and in this the canal was dug to a width of forty feet. Powerful machines that could draw out stumps and pull over the largest trees were brought from Europe. The wheels of the stump machine were sixteen feet across. A plow with a sharp blade was also made, to cut down through the heavy carpet of fibers and small roots.