Dropstone

Dropstones are isolated fragments of rock found within finer-grained water-deposited sedimentary rocks. They range in size from small pebbles to boulders. The critical distinguishing feature is that there is evidence that they were not transported by normal water currents, but rather dropped in vertically through the water column. == Background ==...
Found on http://en.wikipedia.org/wiki/Dropstone

dropstone

(from the article `varved deposit`) ...in recent and ancient sedimentary sequences, where they are often termed varvite, frequently display disruption of the fine lamination and ... ...varves that are laid down in modern glacial lakes at the front of retreating glaciers or ice sheets. Each of these layers defines an annual ... [2 rel...
Found on http://www.britannica.com/eb/a-z/d/76
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