ROBBDiT°^] CLIMATE AND EVIDENCE OF CLIMATIC CHANGES 69 



9. This progressive desiccation, if it has occurred, doubtless has 

 been accompanied by numerous sHght fluctuations in climatic condi- 

 tions, just such as are matters of record during historic time, wet 

 and dry and warm and cool cycles alternating. 



10. Any such progressive change would necessarily be infinitely 

 slow, so that it would not be shown by meteorologic records unless 

 continued through many centuries, with very delicate observations 

 at many stations throughout a large area. 



11 . A natural result of such slow desiccation would be the gradual 

 reduction of the population and the concentration of the remnants 

 in favorable localities. Its effect on the native vegetation would 

 be chiefly in the direction of changing somewhat the boundaries of 

 the plant formations. Its effect on the fauna could not be readily 

 detected except by the discovery of numerous fossils of recent date 

 or by the inferential evidence that might be derived from careful 

 study of the distribution of forms which can not readily migrate 

 over unfavorable areas. 



12. Evidence of recent desiccation is not conclusive, but the 

 problem is probabh^ capable of solution by further cooperative 

 investigation along lines suggested in this discussion. Several 

 lines of evidence point to slight progressive desiccation in the South- 

 west within the period of human occupancy. Such desiccation 

 would satisfactorily account for present conditions, and no other 

 explanation yet suggested seems adequate. 



Suggestions for Futltie Work 



The foregoing summary suggests lines of work for the future, as — 



1 . Keeping accurate records for a long period at numerous stations, 

 of direction, continuity, and force of prevailing winds, temperature, 

 evaporation, and relative humidity. 



2. A thorough study of the ruins and of human remains to ascertain, 

 if possible, what proportion were occupied simultaneously or aban- 

 doned simultaneously, whether abandoned suddenly, and whether 

 general or continued warfare, pestilence, or earthquakes may have 

 aided in the depopulation of the region. 



3. The more complete investigation of the definite traditions of 

 the peoples regarding former climatic and agricultural conditions, 

 mthout unconsciously suggesting to them the answers to inquiries. 

 Also a careful study of old Spanish records and literature of the 

 region ^vith this question in mind. 



4. The careful recording of the fluctuations of land-locked lakes 

 and of the flow of streams, carried on from generation to generation. 



