82 



THE SALTON SEA. 



and porous aggregate. Coating this are usually several concentric layers somewhat similar 

 to the lithoid type. While the columns and plates retain their individuality for the most 

 part, yet they coalesce and anastomose frequently, thus binding the mass into a firm and 



resistant whole. 



Where the tufa is attached to the sides or beneath the boulders the plates and columns 

 are usually more distinctly separated. The projecting shafts and blades bend outward 

 and upward, as if seeking the stronger light. This tendency is the most striking feature 

 of the deposit and the abundant recesses in the cliff gave an exceptional opportunity for 

 thorough observation of this relation. It was found without exception that the tufa turned 

 towards the entrance of the caves in the direction from which the stronger light was com- 

 ing. As the caves penetrated the cliff in all directions this relation of the direction of the 

 growth of the tufa towards the stronger light was tested under all conditions. As the 

 thickness of the tufa developed also depends on the amount of illumination received the 

 influence of light is one of the factors that must be considered in accounting for the origin 



of the deposit. 



Thin sections of the tufa show it to be composed of minute crystals of calcium car- 

 bonate and masses of cloudy material similar to that composing the recent tufa. The thin 

 banding noted in the lithoid type and around the individual plates and columns of the 

 tufa is due to the alternation of denser material with the more porous. Occasional spots 

 of yellow iron stain are found wherever sand grains are included and are a result of the 

 oxidation of the ferromagnesian minerals of the sand. Frequent thread-like lines of slightly 

 darker color, the same size and form of the algae, found in the present tufa and radiating 

 at right angles to the banding, suggest algal filaments. Rarely, in favorable locations, the 

 original algae may be seen preserved in their original position and faint green color. 



ORIGIN OF THE TUFAS. 



The source of the calcium carbonate which forms the greater part of the tufas is found 

 in the waters of the lakes. This is self-evident, since the tufa forms wherever a firm point 

 of attachment is offered, regardless of the lime content of its support. The second column of 

 table 25 shows that the waters of the present Salton Sea contained the stated amounts 

 of calcium as shown by the yearly analyses. From the perennial increase in the amount of 



Table 28. 



calcium, it is evident that the lake waters have not yet reached the point of saturation 

 for the lime. In the third column the percentages of the total solids contained in the water 

 are figured and the partial deposit of the lime is shown. In the fourth and fifth columns, 

 the more significant figures of the carbonate radicle show that it has been decreasing since 

 1908. Assuming for the sake of argument that all of the carbonate radicle was combined 

 with the calcium either as the carbonate or bicarbonate, we find the amounts given m 

 columns 6 and 7 would have been present at the times that the samples were taken. 



Of the two compounds the bicarbonate is by far the more soluble and its solubility 

 is largely increased by the presence of carbon dioxide in the water. If either compound 



