24 trask. PRINCIPLES OF SEDIMENTATION [Ch. 1 



slower or faster rate than it is removed from the beach. (See Chapter 

 15.) In general a sort of dynamic equilibrium prevails. 



Bays 



In areas where sea level is rising or has risen recently, the mouths 

 of streams become drowned and form bays. The tides pass in and 

 out of the mouths of these bays. The water in most bays is shallow, 

 and the diurnal movement of the tide keeps the water muddy. (See 

 Chapter 16.) The position of places of maximum velocity of tidal 

 currents changes from time to time, thus causing continual erosion 

 and deposition of sediment in the bay. Silt and clay are deposited 

 in quiet water, and sand or coarse silt is laid down in or near the 

 channels. The sediments are poorly sorted and vary greatly in tex- 

 ture from place to place. The tidal flats are exposed during low 

 water, and the sediments alternately take on and lose water as the tide 

 comes and goes. Organisms ingest the sediment in search of food. The 

 deposits, therefore, are irregular in character, bedding, and strength. 



Areas of Calcium Carbonate Deposition 



Limestone is formed in several types of environments. Saturation 

 or relatively high concentration of calcium carbonate in the water, 

 however, is common to all types. In addition the rate of influx of 

 terrigenous debris must be comparatively slow with respect to rate 

 of deposition of calcium carbonate. Concentration of calcium car- 

 bonate in water is favored by increase in temperature and salinity 

 and decrease in hydrogen-ion concentration (increase in pH) (Watten- 

 berg, 1933; Trask, 1937). Calcium carbonate may be precipitated 

 directly from supersaturated water; it may be formed by bacteria or 

 algae as a part of the metabolic processes by which the organisms get 

 food and energy from the water; or it may be formed from detrital 

 shell particles. Precipitation of calcium carbonate from saturated 

 or supersaturated solutions is favored by the presence of solid par- 

 ticles of calcium carbonate or other material. In places this process 

 produces small spherical pellets which are called oolites (Brown, 1914). 

 The most favorable environment of deposition of calcium carbonate 

 is a shallow flat-bottomed sea adjacent to a low-lying coast in a 

 tropical or semi-tropical climate, as for example the southern coast of 

 Florida (Vaughan, 1910). Other environments are lagoons, atolls, 

 coral reefs (Emery, 1948), or even the deep sea where the water is less 

 than 20,000 feet deep. (See Chapter 33 in this symposium.) Calcium 

 carbonate may even be deposited from saturated water in lakes (Rus- 



