approximately the value of the producing mines and metallurgical works of the United States at the end of 1916.
In order to arrive at an estimate of the value at the end of 1920 I must proceed in a more empirical way. If the theory that the mines were going to continue their production indefinitely were correct, of course their aggregate value should remain unchanged. However, we know that the mineral wealth of a country is not everlasting. The principle of sustained production that I have previously stated implies the continuance of prospecting and development work, the bringing in of new mines to replace those that have become exhausted. Normally this goes on automatically, but that was not so during the war and the years immediately following. The exigencies of the situation demanded the forcing of production from the developed mines, and scarcely any new mines were brought in. In the case of coal, iron, copper, lead and zinc the production of the mines of the United States during the four years 1917-1920 was in each case about five times the average annual production in tons in the three years 1911-1913. It is a reasonable assumption that if at the end of 1916 the mines of the country could be relied upon for 30 years of production at the end of 1920 only 25 years should be figured. Upon the latter basis a gross yield of 10.095 per cent would be necessary in order to give 7 per cent net and the estimated value of the mines would be $3,268,945,022. The difference between that figure and the one pre- viously given represents the loss of value by depletion.[1]
- ↑ Since making these calculations, which I published in Mining and Metallurgy, for October, 1921, the Census figures for Jan. 1, 1921, have
