u 



Ubiquist (Ubiquitist) 



An organism that flourishes in several kinds of commu- 

 nities or ecosystems, e.g., the raven, red maple tree. 



Ubiquitous 



Refers to a Ubiquist. 



Ultrasonic 



See Supersonic. 



Ultraviolet Radiation 



The electromagnetic waves not perceptible to the human 

 eye, between violet light waves and X-rays, from about 

 390 mu to 10 mu in length. 



Unconformity 



An irregular line of contact between two geological strata 

 caused by exposure to erosion of the lower one before sub- 

 mersion and consequent deposition of the second stratum. 



Underdispersion 



See Hypodispersion. 



Undergrazing 



An intensity of grazing by livestock in which the forage 



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