The Fur Formation is a unit of diatomitic sediment approximately 60 meters thick consisting of diatoms and clay minerals with up to 180 layers of volcanic ash.

The diatomite comprises 2/3 opal tests of diatoms and 1/3 clay, interbedded with layers of volcanic ash and a few limestone horizons ('cementstones'), and has exceptionally complete fossil preservation.

The Fur Formation was deposited just above the Palaeocene-Eocene boundary, about 55 million years ago, and its tropical or sub-tropical flora indicate that the climate after the Paleocene-Eocene Thermal Maximum was moderately warm (approximately 4-8 degrees warmer than today).

The stratigraphy exposed at Knudeklint constitutes the unit that containing the Paleocene/Eocene boundary informally named Stolleklint Clay, which grades up into the Fur Formation.

Most unusual, if not unique, diversity of life from both ocean and land with extremely good preservation of details rarely seen, therefore very reliable reconstruction of palaeobiology.

[3] The earliest Paleogene fauna of any diversity, over 30 species, including some near complete, some preserved in 3-D, and some excellent bird-fossils (even with feathers and chromatine).

[6][21] The following taxa are known:[6][21] Huge fauna from land, over 200 species, many are oldest of their families; many with colour spots and eye lenses, some extraordinary preservation with stridulation (sound) apparatus in grasshoppers, and apparently migratory moth mass mortality.