254 MINERALOGY 



waters are complex solutions of carbonates, sulphates, and chlorides 

 of the more soluble bases, as the alkalies, alkali earths, iron, man- 

 ganese, aluminium, as well as silica and a large number of other ele- 

 ments in very small quantities. The amount of solid residue in 

 the ordinary natural waters will vary greatly, depending upon the 

 nature of the soil and the geological formations over and through 

 which the waters flow. Rivers of limestone regions are usually 

 high in their content of calcium and magnesium carbonates, as 

 these carbonates are carried into solution as bicarbonates and they 

 are termed hard waters. Such waters are not saturated solutions, 

 containing in solids from 10 to 40 parts to the 100,000, unless 

 greatly concentrated by evaporation or by the loss of carbon diox- 

 ide, when the normal carbonates may crystallize or be deposited, as 

 is the case in the formation of stalactites and stalagmites in caves 

 and the calcite cement of some conglomerates. Though the amount 

 of dissolved solids in a river water seems very small, yet when the 

 contant flow is considered, enormous quantities of soluble com- 

 pounds are carried in solution. It has been estimated that the St. 

 Lawrence at Ogdensburg, New York, having a flowage of 248,518 

 cubic feet a second, and a salinity of 13.2 parts per 100,000, will 

 transport by this point, annually, 29,278,000 metric tons of salts 

 in solution. Taking into consideration the area drained, exclusive 

 of water areas, this is equal to, if evenly distributed, 102 tons of 

 matter carried off in solution per square mile each year. The vol- 

 ume of the ocean is so great that its saline content is not apparently 

 increased by these enormous quantities of dissolved salts which are 

 being poured into it by every river; but if at any time such waters are 

 confined and evaporation equals or surpasses the annual addition by 

 rivers and rain, the inclosed lake, basin, or arm of the sea will become 

 concentrated, as in the case of salt and alkali lakes of arid regions. 

 When cencentration advances to saturation, their salts are usually 

 deposited in a definite order, forming stratified deposits, following 

 the order of saturation in regard to the various minerals separated . 

 There is therefore in such saline deposits an order or sequence from 

 the bottom to the top, except where this order may have been 

 modified by some peculiar local characteristic or condition, caused 

 by an unusual component in the solutions. 



When ordinary sea water is concentrated to about one tenth of 

 its original volume, crystals begin to form. In the normal concen- 

 tration of sea water these crystals are gypsum, and gypsum usually 

 forms the lower stratum of such deposits. Anhydrite may re- 



