426 EDWARD STEIDTMANN 



of the sea becomes still more insoluble. The atmospheric condi- 

 tions and the land relief favor the floral blanketing of the earth, 

 thus stimulating chemical denudation and creating an effective 

 screen for the retention of clastic materials on the land. 



As the waters again withdraw from the lands into the hollows 

 of the sea in response to secular earth movements, they leave 

 composite sediments behind them whose ratio of calcium to mag- 

 nesium is higher than that of the average igneous rock. With 

 topographic rejuvenation, the muds are again carried toward the 

 margin and to the deep sea, or possibly at times directly to the 

 deep sea as suggested by submerged stream channels, the con- 

 tinuation of existing streams which in some cases extend to the 

 margin of the deep sea. Various parts of the earth are subjected 

 to regional metamorphism and secular uplift, particularly the 

 continental margins, causing selective removal of calcium and 

 the concentration of magnesium in the residuals. The marginal 

 sediments, dominantly elastics, by virtue of position, relief, and 

 a combination of other factors, are in a most favorable position 

 to be removed from the land and swept into the deep sea, where 

 they would be permanently withdrawn from the land. The depo- 

 sition of elastics is again at a maximum, that of limestones at a 

 minimum. As the pendulum swings from one extreme to another, 

 it marks a curve of progressive change in the composition of the 

 lands and in the ratio of calcium to magnesium in the salts con- 

 tributed to the sea, consummated by an accumulation of limestones 

 on the continents of progressively higher calcium content, both a 

 reflex and a cause of changes in the land composition, and by the 

 withdrawal of the complementary muds toward the margins and 

 the deep sea, slow during periods of oceanic expansion, but tre- 

 mendously accelerated during periods of oceanic retreat, selective 

 concentration of magnesium in the deep zones of high temperature 

 and pressure, in the elastics, and in the sea — a never-ending cycle 

 of selective causes and cumulative effects, recalling the words 

 of Faust: 



Wie alles sich zum Ganzen webt, 

 Eins in dem anderen wirkt und lebt. 



