The yearly output of the anthracite mines is upward of fifty-five million long tons a year, or somewhat less than five million tons per month. In winter the rate of consumption is somewhat greater than that of production. A shortage in the summer production is therefore apt to be keenly felt in the winter. Before shipment to the market the coal is crushed at the breakers, sorted in different sizes, and washed. Most of the anthracite coal-mines are owned by the railway companies centring at New York and Philadelphia, or else are operated by companies controlled by the railways. About one-fourth of the output is produced by independent operators who, as a rule, sell their coal to the railway companies. The Reading, Pennsylvania, Central of New Jersey, Lackawanna, Lehigh Valley, Ontario & Western, Erie, and Delaware & Hudson are popularly known as "coalers" because the larger part of their eastern business consists in carrying anthracite coal. [Illustration: A VIEW OF THREE COLLIERIES IN THE ANTHRACITE COAL BASIN NEAR MAHANOY CITY, PA.] Formerly much of the coal was shipped by canals, but the latter were not able to compete with the railways, and most of the coal-canals have been abandoned. The price of anthracite at tide-water (New York) varies from $3.20 to $4.50 per long ton. At Philadelphia the price is about one-fourth less. Buffalo is the chief lake-port for anthracite. Steam sizes are about two-thirds the price of house fuel. [Illustration: COAL FIELDS IN UNITED STATES] Bituminous, or soft coal furnishes the larger part of the house fuel in the United States, and nearly all the house coal used in other parts of the world. It contains from fifteen to more than forty per cent. of volatile matter, burning with a long and smoky flame. The coal which contains twenty per cent. or less of volatile matter is a free-burning coal that may develop heat enough to partly fuse the ash, forming "clinkers"; it is therefore called "caking" coal, and is not only well adapted for use as fuel and steam-making, but it is also a good smelting coal. Coal which contains more than thirty per cent. of volatile matter is known as "fat" coal and is generally used in the manufacture of coke and illuminating gas. Western Pennsylvania produces the largest amount of fat coal, but it is found here and there in nearly all soft-coal regions. A so-called smokeless bituminous coal occurs in various localities; its low percentage of volatile matter makes it an excellent house fuel. Bituminous coal is mined in twenty-five States of the Union, Pennsylvania, Illinois, West Virginia, and Ohio heading the list. In about half the mines the coal is cut from the seam by means of machinery and is known as machine-mined coal. A very large part of the product is consumed within a short distance of the mines, and this is especially true of the region about the upper Ohio River. [Illustration: COAL PRODUCTION]