52 REPORTS ON INVESTIGATIONS AND PROJECTS. 



This rainy period was both shorter and less intense than the preceding and 

 was followed, in turn, by another but shorter period of aridity and the for- 

 mation of g}'psum dunes ; a short period of relatively higher rainfall, when 

 these dunes were covered and fixed by vegetation, and a later period of re- 

 newed aridity, which is still in progress and during which the present series 

 of moving dunes of gypsum, known as the "white sands," have been formed. 

 Even this last period has not been a unit, having been broken not very long 

 ago by a short period of slightly greater rainfall and of dune vegetation and 

 fixation. The records of this cycle of climatic change and of varying geo- 

 logic action can be read in terraces, arroyos, lake strands, etc., as well as in 

 the gypsum dunes, but are best exhibited in the latter, it being not infrequent 

 to find the four successive series of dunes superposed, the one on the other. 

 These features, as well as the general aspects of the vegetation, afford 

 invaluable comparative data in the interpretation of the phenomena afforded 

 by the Salton. A small number of beach plants or succulents characteristic 

 of saline soils are to be found in both places. Outside of this the species are 

 different, but in their general association they offer landscapes quite like 

 those of the Salton. Succulent desert plants are a small constituent of the 

 floras, and the woody perennials do not reach any notable size. Emphasis is 

 to be laid upon the fact that very few if any species are known which appear 

 to be indigenous to either basin or to have originated there. It is evident 

 that the wide variations in the soil conditions in both basins must operate 

 against the survival of any species unless it is quickly disseminated beyond 

 the borders of the basin, in which case its genetic connection with the locality 

 would be lost. 



REPORTS OF INVESTIGATORS. 

 Changes in Climate, by Prof. Bllsivorth Huntington. 



Dr. Huntington, as a research associate of the Institution, has found it 

 profitable to carry on the major part of his work on variations in climatic 

 factors in cooperation with this department. March and April were devoted 

 to an examination of terraces, ruins, salt lakes, and other material in New 

 Mexico furnishing critical data concerning the course of climate. May and 

 June were spent in California making measurements of cross-sections of 

 giant redwood trees {Sequoia gigantea), for the purpose of ascertaining to 

 what extent possible variations might have been registered by the rate and 

 manner of growth resulting in the annual rings. 



The work in New Mexico began in company with members of the staff 

 of the Desert Laboratory in the Otero Basin, in the southern part of the 

 State, where about three weeks were spent. The two main lines of investi- 

 gation were ruins in the midst of what is now an uninhabitable desert, and a 

 series of gypsum sand dunes and old lacustrine strands which seem to indi- 

 cate climatic fluctuations of some severity since the Glacial period. This was 

 followed by visits to some of the more noted prehistoric sites in the central, 



