[1] The more than 600 metres (2,000 ft) thick formation comprises a rhythmic alternation of sandstones (greywackes and subgreywackes), quartzites, intercalated with siltstones and shales deposited in marine flysch-like environments.

Because of the excellent preservation, including gut remains, of a wide assemblage of early Paleozoic taxa in which trilobites dominate, the formation, which is lean in fossils in many areas but exceptionally rich in what has been interpreted as storm beds, has been designated a Konservat-Lagerstätte.

The Letná Formation was first formally defined in 1966 by Havlíček and Vaněk and crops out in the Prague Basin, a northeast–southwest trending minibasin stretching over 100 kilometres (62 mi) between Rokycany in the southwest and Úvaly in the northeast.

Accumulations of these fossil remains are commonly found in thick-bedded quartzose sandstones of light-grey and yellow or grey-brown color, which might have been deposited in areas sheltered from wave activity by sand bars.

[7] Fossilized gut remains have been observed in four of the about twenty trilobite species present in the Letná Formation: Birmanites ingens, Dalmanitina socialis, Deanaspis goldfussi and Selenopeltis buchi.