on eastern roads like the New York Central, with a large volume of traffic and easy operating conditions. On western lines like the Denver and Rio Grande, in rugged territory, with a sparse population and light tonnage, the per mile rate rises rapidly and the gradation of the general tariff is steep. But always it will be found that the changes in rates occur at competitive points, with transition to a new level of rates determined by the conditions at the next competitive point beyond. An important fact concerning this tariff thus far developed, is that, of course, the height of the upper level at the most remote point must never exceed what the particular traffic will bear. In other words, supposing that the traffic consist of grain or coal, not more than a certain amount could ever be charged, no matter how great the distance, without so far diminishing the profit in the transaction as to render the business impossible. This is shown by the diagram opposite the next page, whereon it appears that each commodity, coal, wheat, cement, lumber, or oil, having attained a certain level of rates, never rises thereafter, no matter what the distance. Each attains the maximum of what it will bear. That level it can never exceed. This immediately leads to another consideration. No single tariff is applicable to any large number of commodities. Each one must be regarded as a law unto itself. Not only does the ultimate amount which each is able to bear depend upon the value of that commodity, but also the conditions determining competition with respect to it must be different all along the line.[70] [Illustration: RATES BETWEEN CHICAGO AND ST. PAUL. DISTANCES IN MILES FROM CHICAGO. RATES IN CENTS PER 100 LBS. [_Facing page 108_]]