Answer:
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.
Dropstones are a smoking gun for indicating a marine or lacustrine environment since they can only be deposited in water.
dropstones can also indicate glacial and iceberg activity. Dropstones only occur where icebergs, calved from glaciers, have passed, so the distribution of dropstones can help paint a picture of their distribution and movement.