68 BUEEAU OF AMERICAN ETHNOLOGY [bull. 54 



Aquatic shells and crustacean remains are found in apparently 

 very recent deposits of several small ephemeral lake basins as far 

 north as northern Colorado, under such conditions as to mdicate that 

 withm perhaps a very few centuries precipitation was sufficient for 

 such forms of life to become established and exist while several feet 

 of fine sediments were accumulating. 



Summary 



1. The climate of the Rito de los Frijoles and surrounding region 

 does not now permit the raismg of corn without irrigation except 

 in perhaps a few favored localities. 



2. Climate has fluctuated throughout the geologic ages, though 

 radical changes need not be supposed. 



3. It would not require a very great increase in precipitation to 

 make the raising of hardy, drought-resisting varieties of corn possible 

 without irrigation in localities where it is not now possible. 



4. Distribution and extent of ruins throughout the Southwest, 

 including the Jemez plateau, strongly suggest different conditions a 

 few centuries ago, with a more general distribution of springs and 

 streams and sufficient precipitation for the cultivation of areas not 

 now fit for agriculture and for the irrigation of tracts where it is now 



^impracticable, thus indicating a probable change of climate within 

 at most the last ten to twenty centuries. There is some direct 

 historical' evidence pointing the same way. 



5. The former existence of extensive lakes where the ratio of evap- 

 oration to precipitation does not now permit them indicates change 

 of climate within a few thousand years, leaving the question open as 

 to whether the change was still in progress during the human occu- 

 pancy of the area dealt with in this paper. 



6. The disappearance of nearly all glaciers from the southern 

 Rockies, including those which existed within a short distance of 

 the Jemez plateau, and the very recent recession of those which 

 remain, together with the fact that they appear to be still receding, 

 indicate a change in climate since a very late period in the Glacial 

 epoch and that probably the change is still in progress. 



7. There is some botanical CAadence, although meager, of a change 

 in clunate within four or five centuries and of the still-continuing 

 desiccation. 



8. On the whole, in the opinion of the writers, various lines of 

 evidence point to progressive desiccation of the region since the 

 beginning of the pueblo and cliff-dwellmg period, with no important 

 evidence inconsistent with this view, although the change in popula- 

 tion may possibly be ascribed to other causes. 



