234 THE WASTE AND CONSERVATION OF PLANT FOOD. 



These authors therefore admit that all the theories so far advanced 

 to explain the magnitude of these deposits are attended with certain 

 difficulties. What, for instance, could have caused a temperature of 

 100°? The most reasonable source of this high temperature must be 

 sought for in the violent chemical action produced by the double 

 decompositions of such vast quantities of salts of different kinds. 

 There may also have been at the bottom of this basin some subter- 

 ranean heat such as is found in certain localities where boric acid is 

 deposited. 



Whatever be the explanation of the source of the heat it will be 

 admitted that at the end of the Permian period there was thrown up 

 to the northeast of the present saline deposits a ridge extending from 

 Helgoland to Westphalia. This dam established throughout the whole 

 of North Germany saline lagoons in which evaporation was at once 

 established, and these lagoons were constantly fed from the sea. 



There was then deposited by evaporation first of all a layer of gyp- 

 sum and afterwards rock salt, covering with a few exceptions the whole 

 of the area of North Germany. 



But around Stassfurt there occurred at this time geologic displace- 

 ments, the saline basin was permanently closed, and then by continued 

 evaporation the more deliquescent salts, such as polyhalite, kieserite, 

 and carnallite, were deposited. 



These theories account with sufficient ease for the deposition of the- 

 saline masses, but do not explain why in those days the sea water was 

 so rich in potash and why potash is not found in other localities where 

 vast quantities of gypsum and common salt have been deposited. It 

 may be that the rocks composing the shores of these lagoons were 

 exceptionally rich in potash and that this salt was, tlierefore, in a cer- 

 tain degree, a local contribution to the products of concentration. 



Through the ages of the past the rich stores of plant food have been 

 steadily removed from arable fields and apparently forever lost. But 

 in point of fact no particle of it has been destroyed. Even the denitri- 

 fying ferments described by Springer, Gay on and Dupetit, and Miintz 

 reduce only to a lower stage of oxidation or restore to a gaseous form 

 the nitric nitrogen on which alone vegetables can feed. But electricity, 

 combustion, and the activity of certain anaerobic ferments herding in 

 the rootlets of legumes and other orders of plants are able to recover 

 and again make available this loss. 



Lately Winogradsky and Warington have shown that an organism 

 can be grown in a sugar solution containing certain salts and exclud- 

 ing all nitrogenous matter save the free nitrogen of the atmosphere, 

 which Is capable of oxidizing and assimilating this inert gas. In a 

 solution containing 7 grams of sugar as high as 14 milligrams of nitrogen 

 have been fixed. 



