The most satisfactory way to describe commercial competition as applied to carriers is by concrete illustrations. There are two distinct varieties or degrees of it, which may be denominated primary and secondary. These might as properly, perhaps, be called simple and complex, or direct and indirect. Of these, the first concerns those cases wherein a commodity undergoes no physical transformation between producer and consumer. Shipments are usually direct. Only one rate is involved. Shall St. Louis and the South, for example, be supplied with salt from the Kansas or Michigan fields?[84] This is a case of pure transportation,--the creation of place value, alone. The Aroostook farmers of Maine compete in prices with the potato growers of Michigan in the New York market. Each district is usually represented by a railway, dependent upon the prosperity of its particular constituency. Competition of markets is usually more keen where a number of carriers are concerned, each representing its own clients; but it may conceivably arise as between several markets served by the same company, especially with the growth of great railway systems. The Southern Pacific must insure a rate from California on oranges to eastern markets, as compared with the rates over the southern roads from Florida, sufficiently low to warrant the venture of capital in the industry.[85] Marble from the quarries of Vermont and North Carolina, and paving blocks from the Lithonia district in Georgia and from Wisconsin or South Dakota, must meet in Chicago on even terms. Such competition, although simple and direct, recognizes no national bounds. Copper from Montana must be laid down in Liverpool at rates to permit of meeting the price on Chili bars from South America. Our entire grain and cotton crops must be transported at rates which will enable them to hold their own in European markets. The California raisin has, in this manner, had to make its way into Eastern markets in the United States against the pressure of importations from Spain, as described in another place.[86] The cotton mills in New England and in the South must have their output carried to China under conditions which will enable them to meet the price made by the British manufacturer. This last instance, however, introduces us to the second form of competition; inasmuch as a double transportation is involved first from the fields to the mill, and thereafter from the mill to the consumer.