556 E. HUNTINGTON SOLAR HYPOTHESIS OF CLIMATIC CHANGES 



to be somehow allied to solar prominences, which in a rough way may be 

 likened to clouds in the terrestrial atmosphere. Perhaps the prominences 

 are more analogous to the clouds of dust sent out by volcanoes than to 

 anything else, but we do not yet know enough of their character to speak 

 at all positively. 



Like the volcanoes and cyclonic storms of the earth, sun-spots appear 

 to be phenomena pertaining merely to the outer layer of the body on 

 which they occur. Their activity varies in much the same irregular way 

 as that of our storms. Roughly they are periodic, but the intervals may 

 be longer or shorter. Volcanoes, too, vary in the same irregular way, for 

 sometimes we have periods of great numbers of eruptions and at others 

 the earth becomes quiescent. Both cyclones and volcanoes can vary 

 greatly on the earth's surface without necessitating any marked varia- 

 tions in the mean temperature of that body and in the amount of heat 

 which it radiates to space. Even the eruption of several hundred square 

 miles of lava would not for any great length of time cause a measurable 

 difference in the amount of heat which would be sent out from the earth 

 to the sun. Such a volcano might erupt again and again at intervals for 

 a century, but even then it would play a small and hardly noticeable part 

 in the gradual cooling of the earth. In the same way there seems reason 

 to think that although the mean temperature of the sun as a whole may 

 remain unchanged, the activity of its surface as shown in the spots may 

 vary as greatly as has the activity of volcanoes on the earth's surface. 



The Connection between jtistokic Ciiangks of Climate and the 



Glacial Period 



Complexity of post-glacial climatic variations in the southwest 



Before turning to the Glacial period let us examine the evidence 

 afforded by the extinct or diminished lakes of the arid regions of the 

 United States. The old strands of such lakes are almost universally re- 

 garded as furnishing one of the most reliable records of ancient climatic 

 variations. The number, relative altitude, and relative degree of promi- 

 nence of such strands, however, may differ greatly in two adjacent basins, 

 even though both have been subjected to the same climatic changes. An 

 example will make the matter clear. Suppose that two basins possess 

 precisely the same climate and are each occupied by a lake 10 miles in 

 diameter. Let there be no difference between the two except that in one 

 basin the lake floor is exceedingly flat, so that the. slope from the shores 

 of the lake toward the center is only 1 foot in 500. In the other basin 

 the floor slopes more decidedly — let us say 1 foot in 25. Let us further 



