80 



THE SALTON SEA. 



Table 26. 



The mineral matter was grouped about the algal threads and partially filled the 

 interspaces. As a result, the tufa is very porous and many vacant interspaces remained. 

 Just beyond the main mass of the deposit minute isolated crystals of the carbonates could 

 be noted attached to the free ends of the algae. 



An analysis of the tufa, by Mr. C. N. Catlin, of the Arizona Experiment Station, 

 shows it to have the composition shown in table 26. 



The undetermined substances were stated to con- 

 sist largely of organic material which it was impossible 

 to separate entirely from the deposit. The analysis 

 shows the tufa to consist essentially of calcium carbon- 

 ate with minor amounts of calcium sulphate and 

 magnesium carbonate. The organic matter was evi- 

 dently the included algae. 



Omitting the undetermined substances and recalculating the analysis to 100 per cent, 

 it is interesting to compare its composition with that of other tufas and a marl deposited 

 in Michigan that has been shown to originate through the activity of algae (table 27). 



Table 27. 



Silica 



Iron and aluminium oxides . 



Calcium oxide 



Magnesium oxide 



Water at 100° 



Carbon dioxide 



Sulphuric anhydride 



Undetermined by difference. 



3.36 

 1.68 



40.65 

 2.23 

 2.02 



33.42 

 2.04 



14.40 



The general similarity in composition of the present Salton tufa to the older tufas 

 of the Quaternary lakes is very striking. Especially noteworthy is the constant small 

 amount of magnesia found in all tufas. The significance of the presence of sulphates in 

 the recent tufa in contrast with its absence in the older deposits can not be stated, but it 

 is not impossible that if the former were exposed to the weather for any length of time the 

 more soluble sulphate would be leached to a large extent. 



The similarity of analyses No. 1 and No. 4 is still more suggestive. Davis 1 has demon- 

 strated that the formation of the Michigan marls is in a large measure due to the activi- 

 ties of both Chara and the blue-green algae. His analysis was made on the material leached 

 by hydrochloric acid from the stems of Chara; and its close similarity to the Salton tufa, 

 both in composition and the close association of the algae with the deposits, implies a 

 like origin. 



Aside from the submerged stems and branches of the dead shrubs about the shores of 

 the lake the only other locality where calcareous deposits are forming at the present time 

 is on the submerged volcanic hills at the southern end of the lake. The writer was unable 

 to visit them, but was informed by Mr. Free that a tufa was there forming on the rocks 

 similar to that found on the shrubs. As far as is known at present, there is no general 

 deposition of calcareous material other than the tufa and no cemented sands or oolites 

 have been discovered on the present beaches. 



1 C. A. Davis, Jour. Geol., vol. vm, pp. 485-497, 1900; vol. ix, pp. 497-506, 1901. 



