Třetihorní subtropy
The Erika Sand Pit
The Erika Sand Pit is known internationally as a locality of Eocene flora.
The fossil plant community of the Staré Sedlo formation bears traces of the
so-called primeval evergreen forests of the subtropical zone. The characteristic
wood species are Daphnogene (Daphnogene cinnamomea), the predecessor of oak
trees (Eotrigonobalanus furcinervis), Laurel (Laurus), Marica (Myrica) or fan
palms (Sabal). The sand quarry provides an ideal location for observation of
various stratification types, bedding and rock structure, which indicate the
mechanism and the environment present during the formation of the strata. It is
the most exposed section of the Staré Sedlo formation, which is the oldest
sedimentary unit in the Sokolov Basin. It was formed in the early Tertiary
Period by fluvial streams and shallow lakes and therefore contains primarily
gravel and sand, which was consolidated in places forming conglomerates and
sandstone. The formation in the sand quarry has an overall thickness of over
20 m. The top 12 m above the groundwater level were subjected to
extraction. 
An
interesting natural environment has developed in the abandoned sand quarry. The
succession processes clearly advanced in the older sections, which have been
covered with Heather (Calluna vulgaris), Silver Birch (Betula pendula), Scots
Pine (Pinus sylvestris) and other species that are adapted to nutrient-poor
stands. Elsewhere the succession has not advanced into the higher vegetation
phase – looser areas without vegetation alternate with grassy sections,
wetlands and water areas. Gradually, vegetation such as bentgrass (Agrostis),
rushes (Juncus), bulrush (Typha) or floating pondweed (Potamogeton natans)
starts to dominate. The damp and humid environment of these biotypes are
appropriate places for the occurrence of amphibians, such as frogs (Rana), the
European tree frog (Hyla arborea), the Natterjack Toad (Bufo calamita), the
Common Toad (Bufo bufo), the Common Newt (Triturus vulgaris) and the Great
Crested Newt (Triturus cristatus). From May until August, a colony of Sand
Martins (Riparia riparia) settles in the sand quarry, boring long nest tunnels
into the quarry walls. 
