Definission: A depression caused by erosion by water or ice. Low-lying land bordered by higher ground; especially elongate, relatively large gently sloping depressions of the Earth's surface, commonly situated between two mountains or between ranges of hills or mountains, and often containing a stream with an outlet.
(Ohio State University Acarology Laboratory, Columbus, OH (OSAL)) - Ohio State Acarology Laboratory (OSAL), Ohio State University {http://www.biosci.ohio-state.edu/~acarolog/collection}
