The salt of Michigan, if the present rate of production of two billion pounds a year is not too greatly exceeded, might probably last some two million years. Yet the consumption will increase—we know not how much, and a much less time and amount would threaten the collapse of Detroit beneath Lake Erie.
They talked only a few decades ago of inexhaustible supplies of iron ore, and yet now a pretty well posted man says there is in sight but thirty or forty years' supply of ore—that is now merchantable, I presume he means. I would double that and say that, at the present rate of consumption of some 23,000,000 tons a year, there is probably enough for eighty years' consumption. Still that is not a very long time in the lifetime of a nation.
One thing must be noted in regard to this matter of exhaustion. It is rare that a resource supposed to be inexhaustible comes so sharply and entirely to an end as the pine of the Saginaw Valley (the American Lumberman says that pine is on the toboggan), or the countless herds of buffalo of the western plains, which were sharply wiped out between 1877 and 1887, so that the buffalo coats which the street car men wore when I was a sub-freshman were a luxury of the rich when I was graduated. Usually as the cost increases it tends to cut down the consumption until a certain balance is attained depending upon available substitutes, and so the price slowly rises and consumption keeps on decreasing. That is the way in which our anthracite coal fields, and the British coal and iron ores are now becoming exhausted; a large part of our anthracite now comes from fine stuff formerly thrown away. Moreover, in many cases there may be both an accumulated stock and a continuous supply. For instance, it is so to a certain extent with our forests. The magnificent growth the pioneers found here was an accumulated stock. But in many countries forests, like a farmer's wood lot here, are looked to for a continuous supply. We must soon be in that case. Originally the great white pine belt extended over 400,000 square miles and there may have been 700 billion feet of it at the beginning, say in 1851. By 1901 there was but 110 billion feet, which was going at the rate of seven billion feet a year.
So within ten years there will be no more white pine—it will be hemlock, jack pine, anything. As the annual consumption in the United States is some 25 billion cubic feet, and the total forest area of the United States is some 500 million acres, from which American lumbering practise will only get 420 board feet a year, it is obvious that even though we improve to the standard of the German practise of 660 board feet per annum, we must still either reforest large areas or find substitutes. It is difficult to see the national economy of rushing through, our timber pellmell at a low price and then buying that of our neighbor, Canada, at a high price.
Besides stored up treasures of wood and coal, the loss by extermina-
