Complexities in rate adjustment often arise from the fact that in the manufacture of many commodities the marketing of by-products is of increasing importance. The rate on the whole series of related commodities must be taken into account at once. Thus in lumbering, a large amount of waste or very low-grade lumber is necessarily produced. This common lumber cannot bear long transportation; it must be utilized locally, if at all. On the other hand, the choicest specialties will command a price even in remote markets. A monopoly price is enjoyed in such a case. The Pacific coast lumbermen can market their long timbers anywhere in the United States; but the demand for the common lumber, restricted to a sparsely populated region, tends to be exceeded by the supply.[116] The real competition between the southern, the Michigan, the Wisconsin and the Pacific coast manufacturers thus narrows down to the sale of the medium-grade product. And the cost of production of this is, of course, in part dependent upon the profit made upon the other two sorts, each of which in its own field appears to be a monopoly. A wide market and a good price for medium-grade lumber may so lessen the cost of the cheapest by-products that they in turn may be so reduced in price as to widen their reach to the consumer. Each rate reacts upon the others. The situation can be successfully controlled only by adjusting them all at once. Not only are rates competitive as between raw materials and the finished product made from them, but the circle of competition immediately widens to include all commodities capable of substitution one for another.[117] Coal rates, of course, are partly determined by rates on cordwood, and _vice versa_. During the great coal strike in Pennsylvania in 1903, soft coal rates and hard coal rates were sadly disturbed. Such substitutions are always likely to occur. But the conditions are not always so simple as this. An instance in point is given by a witness before the Senate (Elkins) Committee on Interstate Commerce in 1905.[118] This shows how a reduction in the rate for transportation of corn from Kansas to Texas brought about a corresponding reduction in the rate on flour from Minneapolis to Chicago. There was a large crop of corn in Kansas; and the Chicago lines anticipated brisk business in the carriage of this product. The traffic managers of lines from Kansas to Texas, however, discovered a large demand for corn in Texas at a price higher than then prevailed in Kansas. Any rate less than the difference in prices between the two districts would cause shipments of corn to flow from Kansas to Texas, just as inevitably as water flows down hill. This rate would needs be low; but the corn could be loaded on empty southbound cars which had been used to haul cotton out of Texas to the north. This, of course, entailed a diversion of corn from the Chicago railways, which promptly reduced rates in order to hold their traffic. For years the