Page:Popular Science Monthly Volume 82.djvu/320

316 of drier years, and which are, therefore, more, or less, favorable to forest growth?

The historical argument may be illustrated by the following:

Clearly, we have nothing beyond the merest hearsay evidence in all this, and absolutely no facts upon which to base a scientific conclusion. Again, in regard to Greece:

Those with even an elementary knowledge of the climatic zones will recall that Greece, like northern California and northern Africa, lies in the subtropical belt, whose dry, or even wholly rainless summers, depend upon the great controls of temperature and pressure and winds and storm-tracks, far and away beyond the reach of any such insignificant local agencies as a few trees.

Or again:

This is a good example of the weakness of the historical argument, even when apparently based upon actual observations.

We might cite further the rather hackneyed examples from Trinidad, where the cause of a general but rather slight decrease in the mean annual rainfall for ten-year periods between 1862 and 1891 (from between 66.50 and 67 inches at the beginning of the period to slightly over 65 inches at the end) has been "said to be the disappearance of the forests"; from Kimberley, where the cutting down of trees to supply timbers for the mines is supposed to have had "most injurious effects on the climate," increasing the number of dust-storms, among other effects; from Ismailia, where tree-growth since the opening of the