PROCEEDINGS OF THE ELISHA MITCHELL SCIENTIFIC 

 SOCIETY, OCTOBER 11, 1921, TO JUNE 2, 1922 



250th Meeting— October 11. 1921 



Collier Cobb — Physiographic Process f^ in Relation to Harbor De- 

 velopment and Harbor Maintenance. 



The observations on which these studies are based have been ex- 

 tended over practically the entire northern hemisphere, and the pro- 

 cesses considered are here presented merely in outline. The object of 

 these studies has been to examine into the physical conditions and 

 the physiographic processes that have to do with the formation, pres- 

 ervation, and destruction of harbors. The pursuit of this object is 

 facilitated by a tentative classification of these sheltered waters, based 

 upon the circumstances of their origin ; and this leads to an at- 

 tempted grouping of those various forms of energy, operating upon 

 and within the earth, which tend to improve or to destroy harbors; 

 and, lastly, it is purposed to consider to what extent these natural 

 processes may be affected by the cooperation of man, or by the 

 hindrance that he may offer to Nature's operations. 



The forces at work upon our shorelines include all of those agencies 

 for the application of solar energy which are generally described as 

 gradational, resulting in the disintegration of rock-masses, and the 

 transportation and deposition of detritus. These atmospheric and 

 aqueous agents effecting gradation may be considered in the follow- 

 ing groups: 1. The work of the atmosphere; 2. Rain and rivers; 

 3. Snow and ice : 4. Wind and waves ; 5. Tides and currents ; 6. Plants 

 and animals. A comparison of harbors of sub-arctic regions with 

 those of sub-tropical and tropica] regions, in essentially similar rocks 

 and rock-structures, will at once reveal the interesting fact that har- 

 bors owe their chief characteristics to the processes by which they 

 have been formed, rather than to the geological formations out of 

 which they have been carved. 



Besides the forces of gradation just enumerated, which have to 

 do with the application of solar energy, there is another group of 

 agents deriving its energy from the earth itself. This comes from 

 the slow cooling of the earth's mass, its warping, and the creeping 



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