36o PRINCIPLES OF STRATIGRAPHY 



salt beds whereupon crystals of salt form in the clayey deposits left 

 on drying of the water bodies. Salt crystals or the molds they occu- 

 pied are common in many ancient deposits, for which a similar origin 

 may be assumed. 



Salt is deposited in the shallow marginal portions of the great 

 Salt Lake of Utah in spite of the fact that the salinity of the lake 

 as a whole is only 230.4 permille. Greater concentration exists, of 

 course, in the shallow marginal pools. In South America salinas are 

 extensively developed in Patagonia and elsewhere. Darwin (14:7(5) 

 describes one of these as consisting in winter "of a shallow lake of 

 brine, which in summer is converted into a field of snow-white 

 salt. The layer near the margin is from, four to five inches thick, 

 but toward the center its thickness increases. This lake was two and 

 a half miles long and one broad. Others occur in the neighborhood 

 many times larger, and with a floor of salt, two and three feet in 

 thickness, even when under water during the winter." Analysis of 

 this salt gave only 0.26 per cent, of gypsum and 0.22 per cent, of 

 earthy matter. The borders of these salinas are formed of mud in 

 which crystals of gypsum up to three inches in length occur. 

 Crystals of sulphate of soda lie scattered about on the surface, and 

 among these the mud was thrown up by numbers of some kind of 

 worm, upon which the flamingos, which frequent these salinas, seem 

 to feed. As already noted, this salt is extensively deposited on the 

 floor of the Karabugas Gulf, where a layer seven feet thick covers 

 an area of 1,300 square miles. Shunett Lake of Siberia also de- 

 posits this salt. 



The "Salitrales" of Patagonia. These should be mentioned in this 

 connection. They are most abundant near Balija Blanca. "The salt 

 here, and in other parts of Patagonia, consists chiefly of sulphate of 

 soda with some common salts. As long as the ground remains moist 

 in the salitrales (as the Spaniards improperly call them, mistaking 

 this substance for saltpetre), nothing is to be seen but an extensive 

 plain composed of a black, muddy soil, supporting scattered tufts 

 of succulent plants. On returning through one of these tracts, after 

 a week's hot weather, one is surprised to see square miles of the 

 plain white, as if from a slight fall of snow, here and there heaped 

 up by the wind into little drifts. This latter appearance is chiefly 

 caused by the salts being drawn up, during slow evaporation of the 

 moisture, round blades of dead grass, stumps of wood, and pieces of 

 broken earth, instead of being crystallized at the bottoms of the 

 puddles of water. The salitrales occur either on level tracts elevated 

 only a few feet above the level of the sea, or on alluvial land bor- 

 dering rivers." (Darwin-14, Chapter IV,) At a distance of some 



