244- D. T. MacDougal—The Salton Sea. 



from a fresh to a brackish condition, and finally concentrate to 

 crystalline salt. These included species of Dunaliella, 

 Pyramimonas, and a red chromogenic bacterium none of 

 which, however, have yet been found in the Salton. 



An examination of the portion of the basin below the 

 ancient beach line and above the present level of the lake leads 

 to the conclusion that the vegetation which was destroyed 

 when the lake was formed included about 8 species of trees, 

 33 shrubs and woody perennials, and 81 herbs, most of which 

 were of the characteristic desert types and hence were sparsely 

 distributed over the 450 square miles that were submerged. 

 The shores of the present lake cut across various soil forma- 

 tions and slopes with gradients ranging from 1 in. 8 or 10 to 1 

 in 300 or more. The yearly recession therefore laid bare an 

 encircling strip which varied in width from a few feet to three 

 or four hundred yards. 



Four main observational areas were selected along the shores 

 and the yearly extensions of these were followed down the 

 slopes as the lake receded in order to ascertain the mechanism 

 of re vegetation of such emersed areas. The following con- 

 ditions had to be considered at every stage of the process : 



1. The observational areas selected represent widely differ- 

 ent habitats as to soil composition and other environic factors 

 or components. 



2. The lake rose quickly to its maximum level and receded 

 rapidly. 



3. The infiltration and leaching of the soil varied year by 

 year as affected by the concentration of the water on one hand 

 and the time of submergence on the other. 



4. The salt content of the water was least during 1907 and 

 increased about 18 to 20 per cent in each succeeding year. 



5. Every emersed strand would therefore be saturated with 

 a soil-solution resulting from the infiltration of the lake water 

 of the concentration and composition prevalent in the period 

 preceding emergence. 



6. The desiccation of the emersed strands would proceed at 

 a rate determined by the character of the soil and by the com- 

 position of the infiltrated water. 



7. The rising water of the lake picked up seeds lying on the 

 surface, and their survival constituted a means of revegetation, 

 chiefly of the strand bared in 1907. 



8. The rates of evaporation and of recession of the lake 

 varied with the season ; being most rapid in June to August 

 and slowest in December and January. The possible total 

 may be estimated at 116 inches per year. 



9. The rainfall data of the Sink, obtained from the records 

 of the U. S. Weather Bureau made at Indio, which is located 



