344 



EDWARD STEIDTMANN 



keynote of their activity is adaptation rather than control. The 

 selection of potassa rather than soda by the land plants and the 

 selection of soda in preference to potassa by marine plants has been 

 cited as evidence for the adaptation of life processes to chemical 

 environment. The preference of lime-secreting organisms for 

 calcium rather than for magnesium may be a similar adaptation. 

 It is suggestive that calcium carbonate is the principal salt contrib- 

 uted to the sea, and that in localities most favorable to life, lime 

 carbonate is the most insoluble of the important salts of the sea. 

 Recent biological studies have also shown that magnesium salts 

 are to a certain extent deleterious to life processes. While the 

 relation of life processes to environment is problematical, the 

 evidence favors the physical control of life processes, rather than 

 the control of environment by life processes. 



Even if the immediate control of the evolution of carbonate 

 rocks was largely by organic agencies, the causation of the control 

 may logically be looked for in the environment. The change in 

 the calcium magnesium ratio, which characterizes the evolution 

 of the carbonate rocks, suggests under this hypothesis that it is 

 related to a similar change in the calcium magnesium ratio of the 

 materials contributed to the sea. It has been indicated already 

 that waters containing. a high proportion of magnesium to calcium 

 are more efficient in causing the development of dolomite than 

 those which do not. The salts of the sea are inherited from the 

 metamorphic processes which have worked the earth over and over 

 again. The circulation of the rock materials from one environment 

 to another involves adaptations. The materials adapted to the 

 new conditions tend to be stable. Others undergo conversion to 

 new mineral forms. Some, finding no place in the new environment, 

 are expelled and may finally reach the sea, where they again under- 

 go environmental adaptations. Could it be possible that the ratio 

 of river-borne calcium to magnesium, which is now approximately 

 6 to i, has undergone an evolution throughout geologic times 

 marked by a gradual increase in calcium and decrease in magne- 

 sium ? A progressive change in the proportions of calcium and 

 magnesium contributed to the sea might have been consummated 

 either by a progressive change in the agents and processes of 



