run-off water and diverting the flow across the slope, thus 

 controlling erosion, cf. Bench terrace. 



Rift Valley 



A long, narrow valley between two approximately parallel 

 geological faults, e.g., the extensive one extending from 

 Lake Nyasa northward in the eastern part of Africa. 



Rill Erosion 



The removal of soil by running water resulting in the 

 formation of shallow channels that can be smoothed com- 

 pletely by cultivation in the normal manner, cf. Gully ero- 

 sion, Sheet erosion. 



Rime 



A feathery or rough layer of ice deposited on plants and 

 other objects by a fog. cf. Hoarfrost. 



Riparian 



Refers to land bordering a stream, lake, or tidewater. 



Riprap 



Stones placed on the face of a dam or on stream banks 

 or other land surfaces in order to protect them from erosion; 

 often applied also to other materials that are used for erosion 

 control. 



Riverwash 



Barren alluvial land exposed along streams at low water 

 levels. 



RNA (Ribose Nucleic Acid, Ribonucleic Acid) 



A nucleic acid occurring in the cytoplasm of plant and 

 animal cells. 



Roaring Forties 



Strong westerly winds over the ocean between latitudes 

 40 S. and 50 S., or the region in which these winds occur. 



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