ipis-] SCHUCHERT— BLACK SHALE DEPOSITION. 269 



geologic time. In such stagnant areas, be they small or large in 

 area, or shallow or deep, the oxygen is soon consumed by the or- 

 ganisms of the benthos and the depths become stale and lifeless. 

 As the sulphur bacteria are ever present, but thrive best in the 

 stale bottoms, they soon take the ascendancy there and fill the 

 waters with an ever greater quantity of sulphuretted hydrogen, pro- 

 vided they are furnished with the dead organisms on which to feed 

 and thus to increase in number. On the other hand, the sun-lit, 

 aerated surface waters are the realm of the green and assimilating 

 micro-plants, the free algae, which convert the inorganic carbon 

 dioxide into their organic bodies, and these upon their death rain 

 into the deeps to form the essential food of the bacteria of the foul 

 bottoms. 



That depth of water is not the first essential for the production 

 of foul bottoms has been shown by the examples cited (almost from 

 the surface down), but it does seem that large areas must have 

 depths greater than 300 feet, for otherwise the high waves gen- 

 erated by the storms would set up a vertical circulation and so at 

 least periodically replenish the oxygen and take away the foul gases 

 of these depths. Therefore it would seem that Black Seas of large 

 size should be deep (300 feet or more) and land-locked basins 

 whose oceanic connections are more or less cut off by submerged 

 barriers. Smaller areas are the elongated troughs and rounded 

 holes below the general level of the sea floors, while the smallest 

 and shallowest areas are the bays that are more or less separated 

 from the seas by closely approaching headlands, banks, and bars, 

 or the marine swamps that are filled with eel-grass, mangroves, and 

 other modified land plants. 



