Another good example of a boulder sized dropstone deposited in the glacial mud. This boulder is a piece of dolomitic limestone, which forms in warm shallow seas.  A current theory suggests that the earth lurched from an "icehouse"  to a "greenhouse"  several times between 760 million and 550 million years ago.  This might explain why limestone blocks with fossil algae called stromatolites  are embebbed in the glacial mud.