The Černé rokle – Black Ravines are of international stratigraphic importance with a stratotype of the boundary between the Lochkov and Prag Formations, as well as being a notable paleontological locality.
The national nature monument lies in the parishes of Kosoř and Radotín on the south-western fringes of the city of Prague. The monument was declared in 1970 and covers an area of 13.26ha at elevations of 230-345 metres above sea level.
The geological basement of the territory is easily visible in the abandoned quarries and on natural rocky outcrops. This area is built of Lower Devonian limestones of the Lochkov and Prague Formations. The boundary between these two levels can best be seen in the abandoned quarries in the north-western part of the protected area. The original stratotype of this boundary was defined here in 1958. This profile is among the most thoroughly researched profiles of this boundary in the world and also serves as a stratotype of the boundary between the Lochkov and the Prague Formations.
The older Lochkov Strata is built of dark-grey to black, very fine-grained limestones with bodies of dark-coloured calcareous shales. These are the Radotín limestones of the Lochkov Formation. The varying grain sizes in the limestones and the bodies of shales bear witness to the activities of marine currents, which intermittently deposited coarser and finer materials, probably due to climatic changes. These Radotín limestones are rich in fossilized remains of brachiopods, large molluscs, gastropod, nautiloids and trilobites. The rarest fossils are the remains of armour-plated fish and parts of the shells of arthropods which were more than 1 metre in length.
The Lochkov Formation is completely overlain by the younger Prague Formation, which is represented by Dvorecko-Prokopský limestone facies. This is a light-grey muddy limestone with a distinctly tuberous structure. The regular interbedding of layers with varying proportions of clay content probably also reflects periodic climate changes.
A global shallowing (fall in the sea level) took place on the boundary of both formations and this is known as the Lochkov-Prague boundary event. The upper Dvorecko-Prokopský limestones were laid down in a calm and deeper environment, with limited effects of marine currents. These limestones are exposed in the abandoned quarries, and also emerge form the natural outcrops at the “V sudech” locality above the first houses in the village of Kosoř. However, these Dvorecko-Prokopský limestones contain fewer fossils.
Non-forest vegetation predominates on the territory with predominantly south-facing slopes falling into the valley of the Kosořský (Šáchetský) potok Stream. On the drier upper sections of the slopes we can find xerophilous and thermophilous grasslands, with rocky steppe communities around the natural rocky outcrops. Very small areas are also covered with downy oak (Quercus pubescens) stands. Fringe shrub communities with a rich herb layer and of great botanical value have developed along the boundaries of the forest stands and the grasslands and in other suitable places. A large number of endangered species, such as the dark-red helleborine (Epipactis atrorubens), have been recorded in these biotopes. As the species-rich grasslands are not grazed by livestock, the grassland growths are gradually becoming overgrown by species-poor thermophilous shrub growths. The greatest disturbance to the vegetation cover of the territory is caused by the planted stands of false acacia (Robinia pseudoacacia) and non-indigenous Austrian pine (Pinus nigra). Most of the natural forest stands are restricted to the damper lower valley slopes, where we can find oak-hornbeam stands with a relatively poor herb layer, with fragments of alluvial forest along the stream valley floor.
The national nature monument plays host to a rich invertebrate fauna. The butterfly populations have been studied in detail. The swallowtail (Papilio machaon), common grayling (Hipparchia semele), safflower skipper (Pyrgus carthami), red-underwing skipper (Spialia sertorius) and the clearwing moth Pennisetia bohemica can all be found in the “Black Ravines”. A notable species of the rocky steppe is the owlfly Ascalaphus macaronius. The occurrence of several gastropod species is an indicator of the quality of the natural environment. A typical reptile on the rocky steppe is the smooth snake (Coronella austriaca). The European eagle owls (Bubo bubo) which nest here are of ornithological significance. Among the mammals, there is an unusually large population of stone martens (Martes foina) in the protected area.