THE TUFA DEPOSITS OF THE SALTON SINK. 



83 



Table 29. 



Calcium carbonate 20° C. 1.2 parts per 100,000. 



Calcium bicarbonate 15° C. 



o.c. COi per 100 c.c. 



1.72 

 0,79 

 0.41 

 0.25 

 0.08 

 0.00 



Ca(HCOa)i per 100.000 



133.1 

 124.9 

 82.1 

 59.6 

 40.2 

 38. S 



is present in the water it is probable that it is the bicarbonate. The solubility of the 

 calcium carbonates is shown by table 26, taken from Seidell.' 



It is evident that all of the carbonate radicle could not be combined with the lime 

 in the form of the carbonate, for the water would be supersaturated and over 90 per 

 cent of the carbonate would be deposited. It is possible, however, for the bicarbonate to 

 be present, as the water would then contain only a third of the amount possible, even 

 if no carbon dioxide were present. If by any means the bicarbonate should be decomposed 

 to the carbonate a deposit would necessarily result. 

 Owing to the comparative dilute solution of salts in 

 the lake water it is not possible for mass action to cause 

 a deposit and other than simple chemical methods must 

 be in operation. 



Of the various methods by which the decomposition 

 of the bicarbonate may be accomplished, only two (me- 

 chanical agitation and vegetation) need be considered. 

 Since the tufa forms beneath the surface of the water it 

 can not be a result from the evaporation of spray. 



As was pointed out by Gilbert, in his study of Lake 

 Bonneville,^ the thickest deposits of tufa are found 

 where the waves were most active. This is the case with the older tufa of this basin. The 

 deposits are best developed where the waters dashed against the cliffs of Travertine Point 

 and the Santa Rosa Mountains. Nevertheless, the tufa was well developed on the small 

 boulders lying on the gently sloping shores to the south. The essential factor in both the 

 present and older tufas seems to be a firm support. Wherever the Blake Sea washed the 

 unconsolidated sands or easily disintegrated Tertiary sediments the tufa apparently did 

 not develop. This is strikingly brought out in the deposits at Travertine Point, where the 

 sands of the bars connecting the heavily coated cliffs show no evidence of cementation or 

 tufa deposits. The present beach sands similarly show no evidence of the deposition of 

 calcium carbonate, although the tufa is forming on the submerged branches and twigs of 

 the dead shrubs but a few feet away. If the formation of the tufa is due to the agitation 

 of the waves alone it would seem strange that it should be so restricted in distribution. 

 If, on the other hand, the tufa is formed primarily through the activities of the algse its 

 better development where the waves are active would naturally follow, for it is well known 

 that the sedentary aquatic life thrives best where the water is in active circulation. 



The algaj associated with the tufas are known to produce calcareous deposits else- 

 where.' The evident relation of the thickness of the deposit of the older tufa and exposure 

 to light, its growth towards the light, its local development, its uniform thickness over a 

 large vertical range, the abundance of snails implying a food supply, the presence of the 

 algJB, the porous, dendritic character of the deposit — all point to its vegetative origin. 



The details of the process by which the algse decompose the bicarbonates and force 

 the deposition of the carbonates are not well understood and remain to be worked out. 

 When this is done, we can say why and under what conditions tufa deposits are formed. 



' A. Seidell, Solubilities of inorganic and organic substances, pp. 86-88. 

 2 G. K. Gilbert, op. cit., p. 168. 



' W. H. Weed, Formation of travertine and siliceous sinter by the vegetation of hot springs. U. S. G. S., 9th Ann. 

 Rept., pp. 619-682, 1889. See also papers cited. 



J. Tilden, Minnesota Alg.^;, vol. ii, pp. 268-271, 1910. 



C. A. Davis, Jour. Gcol., vol. viii, pp. 495-497, 1900. 



