4/b E. M. KINDLE SEPARATION OF SALT FROM SALINE WATER 



accumulate under subaerial conditions more rapidly than it can be re- 

 moved by denudation in a climate which is far from arid. The Salt 

 River is a small tributary of Slave River, which it joins from the west 

 about 170 miles south of Great Slave Lake. A flat j^lain 4 or 5 miles 

 wide, through which Salt River flows, is characterized by highly saline 

 springs which flow from limestones of Devonian or Silurian age. The 

 region is characterized by a heavy snowfall and a rather large summer 

 rainfall, but the precipitation fails to prevent the accumulation of con- 

 siderable masses of salt near some of these springs. In front of one 

 spring visited by the writer there was a mass of salt about 40 feet by 15 

 feet, with an average thickness of about 10 inches. More than 100 sacks 

 of salt are annually taken from this deposit by the people of the district. 

 But the supply is promptly renewed. A considerable portion of this salt 

 bed rises a few inches above the flat sun-cracked saline mud which imme- 

 diately surrounds it. Most of this salt doubtless accumulates through 

 its mechanical separation by freezing of the saline spring waters during 

 the winter, when temperatures often as low as 60 degrees Fahrenheit pre- 

 vail. It is doubtless also receiving continuous accretions from the saline 

 mud under the deposit in summer; from the spring water flowing under 

 it and from the damp salty mud near by it probably adds constantly to 

 its volume in the same way that the mass of salt which seals the fruit jar 

 in figure 2 was accumulated. 



At La Saline, on the Athabasca River, McConnelP- has reported a 

 small deposit of salt formed by a saline spring, which also deposits gyp- 

 sum and native sulphur. 



The occurrence of subaerial deposits of salt like the Salt River deposits 

 in the Northwest Territory and the separation of salt from salt lakes at 

 winter temperatures in high latitudes place in the category of conditions 

 favoring the natural formation of salt deposits, alongside of high tem- 

 perature and aridit}^, very low temperatures acting under average condi- 

 tions of precipitation. 



Formation of Salt Crystals 



At temperatures of about 85 to 110 degrees Fahrenheit, evaporation of 

 a saturated solution of salt results in the formation on the surface of the 

 brine of cubical or prismatic forms in which the upper surface is depressed 

 into an inverted pyramid. This hopper-shaped depression always de- 

 velops on the uppermost side of the figure and causes it to float during 

 the early stages of crystal growth or until it is overturned, when it imme- 



" Canada Geol. Surv., vol. v, pt. i, 1893, p. 35D. 



