Float Silver from Michigan's Keweenaw Peninsula

摘要

Float silver, like float copper, is named for chunks of that metal that have been torn loose from an outcrop or shallow deposit by an advancing glacier and transported along the base of the thick ice sheet along with other rock fragments and debris picked up by the glacier as it moved across the land surface. The advancing sheet of ice acted like a gigantic meat grinder pulverizing the softer rocks and rounding the more resistant material. On cessation of glacial movement about 10,000 years ago the large mass of ice started to melt and recede.