The second objection is that deserts existed in the past much as at present. This is not a real objection, however, for, as we shall see more fully, some parts of the world suffer one kind of change and others quite the opposite. Moreover, deserts have always existed, and when we talk of a change in their climate we merely mean that their boundaries have shifted. A concrete example of the mistaken use of ancient dryness as proof of climatic uniformity is illustrated by the march of Alexander from India to Mesopotamia. Hedin gives an excellent presentation of the case in the second volume of his _Overland to India_. He shows conclusively that Alexander's army suffered terribly from lack of water and provisions. This certainly proves that the climate was dry, but it by no means indicates that there has been no change from the past to the present. We do not know whether Alexander's march took place during an especially dry or an especially wet year. In a desert region like Makran, in southern Persia and Beluchistan, where the chief difficulties occurred, the rainfall varies greatly from year to year. We have no records from Makran, but the conditions there are closely similar to those of southern Arizona and New Mexico. In 1885 and 1905 the rainfall for five stations in that region was as follows: +------------------------------------------------------------+ | | | _Mean rainfall | | during period | | _1885_ _1905_ since | | observations | | began_ | | Yuma, Arizona, 2.72 11.41 3.13 | | Phoenix, Arizona, 3.77 19.73 7.27 | | Tucson, Arizona, 5.26 24.17 11.66 | | Lordsburg, New Mexico, 3.99 19.50 8.62 | | El Paso, Texas (on New | | Mexico border), 7.31 17.80 9.06 | | ---- ----- ----- | | Average, 4.61 18.52 7.95 | | | +------------------------------------------------------------+