Fossil charcoal is known as fusain, a crumbly silky material which may form blocks or microscopic films.[8] Plants can be preserved in exquisite detail, and original cell structures can often be preserved in three dimensions.[8] Spectacular images can be recovered using scanning electron microscopy.[9] Fragments can be distributed some distance, and soot-rich layers in strata deposited by deltas can provide a 'time-averaged' record of fire activity in the catchment (and up-wind) area of the river.[8]