EVAPORATION OF SALINE WATER 475 



salt district appear to afford examples of such migration of salt upward 

 in great quantities. Isolated domelike masses of salt more than 2,000 

 feet thick occur there in beds of Quaternary age^ which have evidently 

 been derived from older beds through the agency of salt-bearing waters 

 rising along fault-planes and depositing their salt at the intersection of 

 the faults/ The salt hill south of Algiers, in Africa, which has been de- 

 scribed by Ville,^ appears to be another example of a great secondary salt 

 deposit. 



The shallow salt lakes of northern Patagonia, with floors of salt 2 or 3 

 feet in thickness, described by Charles Darwin,^ illustrate the conditions 

 under which some of the continental deposits of salt are now accumu- 

 lating. 



Salt Separation by Freezing 



It is a familiar fact that the freezing of saline water is accompanied by 

 a partial mechanical separation of the salt. In the case of sea-water, 

 Mawson,^^ in recording his observations in the Antarctic on this subject, 

 states that "the sea-salt mechanically separates from the ice as the latter 

 forms and is partially forced out into the sea-water below and partly in- 

 cluded in white, vertical tracts between the ice prisms. . . . During 

 the formation of surface ice some of the sea-salts are squeezed upward 

 through capillary cracks to the surface and then, in the form of concen- 

 trated brine, eventually freeze as cryo-hydrates and form nuclei from 

 additions from atmospheric water vapor." These a;re the ice-flowers of 

 Captain Scott.^^ Eegarding the salt lakes of the Antarctic, Mawson re- 

 ports that "as refrigeration goes on in the lakes, the saline contents are 

 gradually concentrated in the residual liquid and a continuously increas- 

 ing cold is required to freeze each succeeding separation. Ultimately a 

 meshwork of ice and cryo-hydrate crystals are formed at the bottom of 

 the lakes. As some of the lakes are very saline, this cryo-hydrate often 

 bulks large. Some of it freezes at as low as a temperature of 50 degrees 

 Fahrenheit below freezing point." 



A salt deposit in the Salt River valley of the Northwest Territory, 

 Canada, which was recently examined by the writer, shows that small 

 deposits of salt may, chiefly through the freezing of salt spring water, 



8 G. D. Harris : Bull. Geol. Surv. of Louisiana, No. 7, 1908, pp. 15, 24. 

 ^ Ibid., pp. 79-81. 



8 Ann. des Mines, 5th ser., vol. 15, 1859, p. 365. 



9 Jour. Researches during the voyage of the Beagle, 1860, p. 75.' 



10 Douglas Mawson : Notes on physics, chemistry, and mineralogy. The heart of the 

 Antarctic, by E. H. Shackleton, vol. iii, 1909, pp. 354-359. 



" Capt. R. F. Scott : The voyage of the Discovery, vol. I, pi. opp. p. 268. 



