524 THE GLACIAL LAKE AGASSIZ. 



covered this area and were plowed up liy the ice-sheet, mixed with mucli 

 drift from the region of granites, gneiss, and crystalhne schists on the 

 nortlieast, and redeposited as tilh The soluble alkaline ingredients of 

 the soil impregnate all the waters of wells, springs, and streams in this 

 region ; and in the dry season they are often seen forming a white or gray 

 efflorescence on the surface of the land, resembling frost, sometimes a 

 quarter of an inch thick, being the residue from the evaporation of mois- 

 ture rising through the j^orous ground.^ 



Wheat thrives better where the soil contains a considerable proportion 

 of these alkaline salts, so that their presence throughout the Eed River 

 Valley is one principal cause of its superiority in wheat raising; and this, 

 grown year after year, gradually takes away these ingredients and pre- 

 pares the land for other crops. But their eflFect as dissolved everywhere 

 in wells and streams partly offsets this benefit, and makes the water of all 

 this region objectionably hard, and sometimes in wells and springs notice- 

 ably bitter or salt. 



The hardness of the water, on account of which it will not dissolve 

 soap, is produced by the carbonates of lime and magnesia, which it has 

 taken up in soaking through the ground. The best wa}- to provide water 

 satisfactory for washing with soap is by collecting the rain from roofs. By 

 the construction of cisterns, this soft water, wliich also is preferable for 

 drinking and cooking, may be kept constantly on hand, there being gener- 

 ally a good supply of rain in all seasons excepting winter, wlien it falls as 

 snow. 



The water of streams and wells in this district contains a small pro- 

 portion (if the alkaline sulphates of lime, soda, magnesia, and potassa, and 

 carlionate of soda, though not usually enough to be perceptible to the 



'An analysis, by Prof. .James A. Dodge, of an " alk.ali " efflorescence from a surface of till in 

 Murray County, southwestern Minnesota, showed it to be a hydrous sulphate of magnesia, with 

 slight traces of soda, potash, .and limo. The proportions of sulphur trioxide and magnesia were the 

 Slime as in epsomite (epsom salt), but it had less than half the percentage of water of crystallization 

 required by epsomite. (Geol. ami Nat. Hist. Survey of Minnesota, Tenth Annual Report, for 1881, 

 p. 202. ) 



Efflorescent saline matter from one of the alkaline lakes of the Missouri Coteaii, .analyzed by 

 Dr. O. M. Dawson, contained of sulphate of magnesia, 49.06 per cent; sulphate of sod.a, 47. 7S per 

 cent; and cliloriile of sodium, 0.7."i per cent. A simil.ar saline incrustation from the Souris Valley, 

 examined qualitatively by Dr. Dawson, .showed only the magnesic and sodic sulphates. (Geology 

 and Keaources of the Forty-ninth Parallel, p. 293.) 



