58 REPORTS 05* INVE:STIGATI0NS AND PROJECTS. 



includes Obsidian Island, lying offshore from No. i about 5 miles southwest 

 and separated from it by a sheet of water with a maximum depth of 30 feet. 

 No. 3 is situated at the extreme northAvestern end of the lake and is covered 

 wih a dense jungle of mesquite (Prosopis), salt-bush (Atriplex) , and salt- 

 grass (Distichlis spicata). No. 4 comprises the wide floor of a desert wash 

 and adjoining shores near Travertine Point, on the southwestern side of the 

 lake, and bears Parosela, Gaertncria, and other plants native to dry soils 

 fairly free from alkali (plate 4). No. 5 lies a short distance to the south- 

 ward of No. 4, and offers especially good opportunities for the study of the 

 conditions which lead to the development of beach-lines, marked by zones of 

 vegetation, which maintain their individuality many years after the recession 

 of the water. No. 6 includes an area among the sands of Carrizo Creek, 

 characterized by moving crescentic dunes and by stationary mounds moist 

 with saline and alkaline water and bearing numerous small shrubs. 



The vegetation now occupying the various sections is largely determined 

 by the amount of soil-moisture and the proportion of salts present, which 

 are chiefly the result of the leaching action of meteoric factors. The sub- 

 merged areas are of course saturated with the water of the lake, which showed 

 the following constituency in a sample taken from over the deepest part of 

 the lake, June 3, by Prof. V. M. Spalding, which was analyzed by Prof. R. H. 

 Forbes and Dr. W. H. Ross, of the agricultural experiment station of the 

 University of Arizona. 



Total Soluble Solids at 110° C; parts in 100,000. 



Sodium III. I 



Potassium 2.3 



Calcium g.g 



Magnesium 6.4 



Aluminum 0.031 



Iron .005 



Chlorine 169.7 



Sulphuric 47.6 



Carbonic 6.6 



Silicic 1.2 



Phosphoric .018 



Total 364.8 



The proportions of sodium, chlorine, and sulphates present are relatively 

 greater in relation to the other soluble solids than in the water of the Colo- 

 rado River, indicating that other sources, inclusive of the original residue 

 from sea-water and material from the mud volcanoes, are to be considered. 



The emersion of the extensions of the observational areas will bare a soil 

 practically uniform in the salts contained, and the restoration of the plant 

 covering found before the inundation must be preceded by the differential 

 leaching and capillary action which previously resulted in such diversity of 

 soil content. The exact observation of these changes in the soil and the 

 accompanying action of vegetation is expected to oft'er evidence of great 

 value bearing on the factors in the main distributional movements of plants 

 over the surface of the earth. 



The level of the lake having fallen about a foot on June i, 1907, an exami- 

 nation of a portion of the shore line and of observational area No. 3 at Mecca 



