The boatmen owed a grudge to the steamboat, just as the pack-horse men had hated the Conestoga wagon, for they saw that their trade was lost, and it was hard to try to make a living in some other way. For many years the great passenger boats reigned supreme on the rivers of the West, but at last they in turn were forced to give way to the railroads. Such boats still run on the Ohio and the Mississippi, but men do not travel on them when they wish to go quickly. Railroad cars, however, do not take the place of some boats on the Ohio. Look out on the Monongahela at Pittsburg and you may see large fields of boats,--many acres of barges, for there are barges on the river still, though they do not look like the old ones. They are of great size and are sometimes made of steel. The coal, taken from the hill out of which it is dug, is run on a trestle along the river and dumped into one of these boats. At Pittsburg the barges wait for the water to rise to a “coal-boat” stage,--that is, until there is a depth of at least eight feet all the way down the river Then a number of barges are lashed together and a steamboat pushes them down the stream. The water often comes up suddenly, and the coal must be rushed to market while the high water lasts. A single towboat sometimes takes to New Orleans several acres of coal from the great Pittsburg coal seam. This lies flat under the hilltops and is mined from the edges where the rivers have cut down through the coal, far into the beds of rock that lie below. [Illustration: FIG. 46. COAL BARGES, PITTSBURG] On the Monongahela the United States owns fifteen dams with locks, and the river is thus “slacked” far up into West Virginia. The dams change the river into a series of long, still ponds, which are deep enough to float the coal barges. Below Pittsburg, in the Ohio, is another dam which sets the water back and makes a harbor for the city. There is no coal to send down the Allegheny, but there are logs to be rafted, and there is much oil, for the river flows through the petroleum region around Oil City. Some of this is taken to refineries at Pittsburg and made ready for use. Much natural gas is obtained by boring and is used in the city for warming houses and for cooking. [Illustration: FIG. 47. PITTSBURG AT NIGHT]