4 io EDWARD STEIDTMANN 



calcium carbonate may become so unstable through these and 

 other causes as to result in direct chemical precipitation as shown 

 by the well-known case described by Willis 1 in the Everglades off 

 the Coast of Florida and that of Lyell 2 in the mouth of the Rhone. 

 In shallow, warm waters near the lands, the deposition of calcium 

 carbonate through lime-secreting organisms is very much more 

 rapid than in deep waters. 



While 90 per cent of the accumulations of calcium carbonate 

 on the floor of the present deep sea come from the skeleta of free- 

 swimming organisms which thrived within the photobathic zone 

 in shallow waters, the remains of both the free-swimming and 

 benthos organisms augment the rate of accumulation. Further- 

 more, the chances for the preservation of skeleta are many times 

 better in shallow water than in the deeps, as shown by the decrease 

 in the calcium carbonate content of marine deposits with depth. 

 In sinking through miles of water, the remains of pelagic organisms 

 often dissolve before reaching the bottom. Not only is there a 

 very clear dependence of abundant limestone deposition on shallows 

 in the present seas, but from the physical evidence of ripple marks, 

 etc., Schuchert concludes that North American Paleozoic lime- 

 stones were probably all deposited in less than 300 feet of water. 

 The food supply is another very important factor which attracts 

 lime-secreting organisms to warm, clear, shallow seas near the 

 continents. 



The activity of the lime-secreting organisms would be further 

 stimulated by the climatic moderation and uniformity which 

 seem to accompany periods of oceanic expansion. The warming 

 of the seas, consonant with oceanic expansion according to Cham- 

 berlin's hypothesis, would diminish its capacity for carbonic acid 

 and decrease the solubility of calcium carbonate. But the shallow 

 epicontinental sea, it seems, would be most susceptible to solar 

 heating, hence from a combination of causes, mechanical, physical, 

 chemical, and organic, limestone building in the shallow seas would 

 probably be intensified in more than arithmetical ratio to the 

 increase in the area of shallow water. The total contribution of 

 calcium from the land would be lessened because of the decreased 



1 Jour. Geo 1 ., I (1893), 512. 2 Principles of Geology (12 ed.), I, 426. 



