Vocabulary enhancement

Here is a word I learned in the NRCS Soils Survey today:

Varve 

A sedimentary layer or a lamina or sequence of laminae deposited in a body of still water within a year. Specifically, a thin pair of graded glaciolacustrine layers seasonally deposited, usually by meltwater streams, in a glacial lake or other body of still water in front of a glacier. 

(A slightly simpler definition is at Dictionary.com)