558 E. HUNTINGTON SOLAR HYPOTHESIS OF CLIMATIC CHANGES 



the rate of 1 foot in 25 will oblige the water to fall 20 feet before the 

 'evaporation surface becomes small enough to be in equilibrium with the 

 diminished supply of water. If the lake remains at this level for a few 

 decades, distinct beaches and bluffs will be formed, for the lake will not 

 be so shallow as to prevent the waves from breaking on the shore, and the 

 slope of the land will permit wave erosion to proceed rapidly. When this 

 lake disappears, its two positions will be marked by strands whose eleva- 

 tion will differ by 20 feet. These will form a pronounced and easily de- 

 ciphered record of a climatic fluctuation which affected both lakes equally, 

 but whose existence would be quite unknown if only the first of our two 

 basins were studied. 



The importance of these considerations lies in the fact that the basins 

 of our Western States show an extraordinary variation in the number of 

 their old lake terraces. This variation may mean in part that the cli- 

 matic changes of the past, like the little changes of the present, as shown 

 in our maps of rainfall and storms, differed in intensity from place to 

 place. In the quotation which will follow shortly the reader will notice 

 that the greatest number of old strands is found not far from the center 

 of the area shaded black in figures 16 and 17. This is what would be 

 expected, for from the center outward the degree of change diminishes 

 until the zero line is reached, after which it becomes of an opposite type. 

 The variation in the number of terraces also means that topographic con- 

 ditions sometimes favor the preservation of records of slight changes, and 

 sometimes do not permit even the larger changes to leave a permanent 

 record. Hence, if we desire to know the true degree of changeability, we 

 must focus attention on the places where the fullest records have been 

 preserved. 



FREE'S DATA AS TO OLD STRAXDS IN THE SOUTHWEST 



Although the history of the main events in the histories of lakes Bonne- 

 ville and Lahontan is familiar, there are many other old lakes whose 

 very existence is almost unknown. They are now being studied, how- 

 ever, and are giving most interesting results. Probably the most com- 

 prehensive study yet made is that of Mr. E. E. Free, Avho, in his in- 

 vestigation of potash and other salines on behalf of the United States 

 Department of Agriculture, has spent several years in traveling about 

 among the desert basins. He has published a summary of the topo- 

 graphic features of those parts of I^orth America which are without 

 drainage to the sea, and has distinguished 126 basins which are of suffi- 

 cient importance to deserve individual consideration. In addition to this 

 he has most courteously permitted me to use some of his unpublished 



