96 CARNEGIE INSTITUTION OF WASHINGTON. 



area under discussion it will probably be possible to find almost every 

 stage of development, and thus to form a typical series to which playas 

 in other parts of the world may be referred. The second, and more 

 important, problem relates to the chemical composition of the deposits. 

 The various chemical precipitates, such as soda, potash, lime, gypsum, 

 borax, and others, which are laid down when salt lakes evaporate, are 

 most puzzling because they do not follow the laws which seem to be 

 deduced from laboratory experiments. The presence of minute organ- 

 isms is doubtless in large part responsible for this, but the reduction 

 to the playa stage with its alternate drying and flooding may be an 

 important factor. The marked climatic fluctuations indicated by other 

 lines of evidence suggest that the playa stage has been much more 

 common than is generally supposed. 



The Curtailment of Rivers by Desiccation, by Ellsworth Huntington. 



Three main rivers, the Mohave, Owens, and Amargosa, drained to 

 Death Valley at the height of the glacial period. Practically no sur- 

 face water now reaches it. The process by which each of the three 

 rivers has been cut off is typical of what has happened in almost every 

 arid region, and therefore needs no elucidation. Owens River reached 

 Death Valley through a chain of from three to five lakes, which were 

 greatly expanded at the time when the river was largest. The Mohave 

 and probably the Amargosa appear to have had few or no lakes along 

 their courses at the time of their maximum development. Now, how- 

 ever, they are again and again interrupted by lakes or playas which owe 

 their origin to the deposition, by tributaries, of detrital material in 

 the form of fans. 



The Agreement of Botanical, Chemical, and Physiographic Evidences of Climatic 

 Pulsations, by Ellsworth Huntington. 



Perhaps the most important single feature of the year's cHmatic 

 work has been the correlation of diverse types of evidence in respect to 

 the climatic changes of the past 2,000 years. A study of the chemical 

 composition of the salt water of Owens and Pyramid lakes, by H. S. 

 Gale and J. C. Jones, shows that the lakes must have overflowed and 

 been fresh not much more than 2,000 years ago. Old strands indicate 

 that the fall from the outlet level has been pulsatory, that is, the lake 

 level has fallen, then risen toward, but not generally to, the old level, 

 and then fallen again. This has been repeated several times. A com- 

 parison of the strands with the curve of growth of the sequoia tree 

 which grows only 50 miles from Owens Lake, shows that the periods of 

 high water in the lakes correspond closely with those of rapid growth in 

 the trees. The correlation is so close that it is possible to date a given 

 strand within a century or less. Moreover, the same series of strands 

 can be detected not only at Owens and Pyramid, but at Mono Lake, 



