486 BOUNDARIES OF THE SEA 



accumulates as a dense cloud in the salt water wedge and awaits 

 an exceptional ri\'er flow to flush it out to sea. There are many 

 other interesting forms of mixing and of sediment distribution in 

 river mouths. 



The importance of climate to the formation of sediments is 

 obvious. The strength, duration, and frequency of winds, and 

 whether they are onshore or offshore are all-important to wave 

 action. Winds may also cause upwelling and plankton bloom or 

 the reverse. Temperature and evaporation likewise influence 

 \'ertical circulation and the fertility of the water. Precipitation 

 has its most marked influence, like most other climatic factors, 

 in enclosed gulfs. All the climatic factors are of great significance 

 to the biological environment and thus play a part in the produc- 

 tion of shelly materials and particles of organic matter. One can 

 hardly imagine greater contrasts than between the deposits of the 

 sea floor off coral reefs, mangrove coasts, desert shores, temperate 

 dune and rock coasts or arctic beaches. 



In this review of environments several ecological factors have 

 been mentioned. The remains of animals and plants enclosed in 

 fossil sediments form, in fact, one of the most important sources 

 of evidence on the environment of deposition, because organisms 

 are very selective as to their conditions of life. Hence, ecological 

 information, especially on organisms that have hard parts to 

 fossilize, is of the utmost importance to geologists and, as we all 

 know very well, ecologists and sedimentologists have already 

 teamed up in many research projects. 



Marine Geophysics 



Some aspects of the biological, chemical, topographical, and 

 hydrological influences on sedimentation have been reviewed, 

 but the connections between marine geophysics and bottom de- 

 posits are no less close. A few items should be called to mind. 



Seismic measurements of the thickness, stratification, and de- 

 gree of consolidation are among the major sources of information 

 for the sedimentologist. This is particularly true if the latter seeks 

 to tie his subject to the problems of general geology and crustal 



