536 E. HUXTIXGTOX SOLAR HYPOTHESIS OF CLIMATIC CHANGES 



large army accomplished a journey in a place where today even a small 

 caravan nsnally finds great difficulty in procuring forage and water. 

 Moreover, elephants were taken 180 miles across what is now an almost 

 waterless desert, and yet the old historians make no comment on such a 

 feat which today would be practically impossible. These things seem 

 more in harmony with a change of climate than with uniformity. Xever- 

 theless. it is not safe to place much reliance on them except when they 

 are taken in conjunction with other evidence, such as the numerous ruins, 

 which show that Makran was once far more densely populated than now 

 seems possible. Taken by itself, such incidents as Alexander's march can 

 not safely be used either as an argument for or against changes of climate. 

 The distinction between changes of temperature and clianges of pre- 

 cipitation. — The third and last objection which we shall here consider is 

 also the strongest. It is based on the condition of vegetation. The whole 

 question is admirably set forth by Gregory,^- who gives not only his own 

 results, but those of the ablest scholars who have preceded him. His con- 

 clusions are important because they represent one of the few cases where 

 a definite statistical attempt is made to prove the exact condition of the 

 climate of the past. After stating various less important reasons for 

 believing that the climate of Palestine has not changed, he discusses vege- 

 tation. The following quotation indicates his line of thought. I have 

 italicized a sentence near the beginning in order to call attention to the 

 importance which Gregor}' and others lay on this particular kind of evi- 

 dence : 



"Some more certain test is necessary than the general conclusions which can 

 be based upon the historical and geographical evidence of the Bible. In the 

 absence of rain gauge and thermometric records, tlie most precise test of cli- 

 mate is given J)y the vegetation ; and fortunately the palm affords a very deli- 

 cate test of the past climate of Palestine and the eastern Mediterranean. . . . 

 The date palm has three limits of growth which are determined by tempera- 

 ture ; thus it does not reach full maturity or produce ripe fruit of good quality 

 below the mean annual temperature of 69=^ F. The isothermal of 69° crosses 

 southern Algeria near Biskra ; it touches the northern coasts of Cyrenaica 

 near Dema and passes Egypt near the mouth of the Nile, and then bends 

 northward along the coast lands of Palestine. 



"To the north of this line the date palm grows and produces fruit, which 

 only ripens occasionally, and its quality deteriorates as the temperature falls 

 below 69°. Between the isotherms of 68° and 64°, limits which include north- 

 ern Algeria, most of Sicily. Malta, the southern parts of Greece and northern 

 Syria, the dates produced are so unripe that they are not edible. In the next 

 cooler zone, north of the isotherm of 62°, which enters Europe in southwestern 



^ J. W. Gregory: Is the earth drying up? Geog. Jour., vol. 43, 1914, pp. 148-172 and 

 293-318. 



