As the elevators of Chicago represent its traffic in grain, and contain usually a large proportion of what is known as the "visible supply," so do the vast lumber-yards along Chicago River often store up an enormous product of the output from the "Great North Woods," covering much of Michigan, Wisconsin and Minnesota, and spreading across the Canadian border. The third great branch of traffic is represented by the Union Stock Yards in the southwestern suburbs. These yards in a year will handle eight millions of hogs, four millions of cattle, four millions of sheep and a hundred thousand horses, over two-thirds of the hogs and cattle being killed in the yards and sent away in the form of meat, and the whole annual traffic being valued at $250,000,000. The yards cover three hundred acres, and with the packing-houses employ twenty-five thousand men, and they have twenty miles of water-troughs and twenty-five miles of feeding-troughs, and are served by two hundred and fifty miles of railway-tracks. The hog is a potential factor in American economy, being regarded as the most compact form in which the corn crop of the country can be transported to market. The corn on the farm is fed to the hog, and the animal is sent to Chicago as a package provided by nature for its economical utilization. The Union Stock Yards make a complete town, with its own banks, hotels, Board of Trade, Post-office, town-hall, newspaper and special Fire Department. The extensive enclosure is entered by a modest, gray sandstone turreted gateway, surmounted by a carved bull's head, emblematic of its uses. The Horse Market is a large pavilion, seating four thousand people. From this vast emporium, with its enormous packing-houses, are sent away the meat supplies that go all over the world, the product being carried out in long trains of canned goods and refrigerator cars, the most ingenious methods of "cold storage" being invented for and used in this widely extended industry.