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The main differences are that dropstones are 'fossilised' - i.e. contained within a sedimentary rock - and that they are submarine, being carried by floating agents, rather than terrestrial, meaning that glaciers cannot be invoked as a complete transport system (an iceberg stage is required). VerisimilusT 21:33, 28 April 2007 (UTC)
Thanks for the answer. Maybe add that explanation to the article somehow. --126.96.36.199 07:12, 29 April 2007 (UTC)
I'd suggest that this move to a new section of situations that might be mistaken for dropstones, but are not. Turbidity currents can indeed contain large clasts like dropstones, but the clast didn't drop in from through the water column (as required by the name) and won't display the evidence of such. --Zamphuor 13:33, 29 April 2007 (UTC)
I'm not sure how these fall into the definition. As I understand it, some stones dislodged by turbidity currents can transported and fall a number of metres - so whilst not falling through the entire water column their method of deposition is identical for the last few metres of their fall. VerisimilusT 12:14, 2 May 2007 (UTC)