A great natural curiosity of Siedliska are many, often magnificent fragments of fossilized trees. As early as five centuries ago, Jan Dlugosz wrote in his famous "Annals", in the chapter about peculiar things in Poland: "...in forests, in fields and woods of the town of Potylicz and the villages of Hrebenne and Prusie, pine trees have this nature and property that if a part thereof, even a branch or another piece, is cut off or broken off, or even if the entire tree is cut down, it turns into and evolves into flintstone after a few years." Dlugosz was wrong about the time it takes for fossils to develop, but he was completely right recognizing them as a great curiosity of our land. Although these fossils are paleobotanically and geologically extremely interesting, no study is available to describe them in a detailed and complex way. The newest standpoint concerning classification of this wood is given by Marzena Klusek. In his study supported by material examination, she proves that the wood is of Toxodioxylon toxodii Gothan species, as test results proved that all samples had the same type of structure. Further, she explains the conditions in which these fossils evolved: "... Tertiary trees overgrowing river banks and floodland did not need to be transported far away to places where fossilization could proceed, while the marsh environment, owing to high content of organic matter, delayed biological decomposition. An additional factor favouring the preservation of coniferous trees in the fossil condition is resin contained in their wood. This allows the remains to stay for sufficiently long period of time in an environment conducive to mineralization. Fallen trunks were transported to places of accumulation and then covered by sediments. This ensured that oxygen availability was restricted, and thus biological wood decomposition was inhibited. Coniferous trees are also more likely to remain in the fossil condition because their lignin, unlike the lignin of deciduous trees, is decomposed into products that are not soluble in water, and the tissue structure, as a result of small tubule sizes, is less exposed to penetration by detrimental microorganisms. Fossil woods are characterized by siliceous mineralization in its various versions, with the supplementary share of other minerals. They have very different colours - from white-yellowish, through sand-beige (most frequent), reddish (occasionally), grey, grey-brown, to almost black. At the time of tree petrification, silica (SiO₂) released from waterlogged sands, mud, volcanic dust and other formations, penetrated to wood tissue structures, and imbued them, and in extreme cases, replaced a large proportion of organic matter. "The results of mineralogical and petrographic tests of fossilized trunks from Siedliska prove that the products of their mineralization are SiO₂ group minerals (chalcedony, quartz) and alofans. A slight admixture is also organic matter. The degree of SiO₂ crystallization varies, and a few types of them can be distinguished: crypto- and microcrystalline, mid-crystalline and mid-crystalline with quartz veins." (Heflin 1996). The presence of alofans proves that the appropriate quantity of silica available for tree silification resulted from lateritization, occurring in hot and humid climate (Heflik 1996). Fossilized trunks are rarely found in their original deposits. Most frequent are fine wood pieces scattered in surface Quaternary sediments, being a result of destruction of their mother Tertiary level. Found pieces come from Quaternary formations. Wood washed away from Miocene sediments was subject to the destroying effects of airing and erosion. These processes made wood move and break down into pieces. Some pieces have aeolian cut or dessert glaze-like efflorescence on the surface, proving periodical exposure to dry climate. They were probably formed in late Miocene. The degree to which wood structure is preserved differs both within different samples and single trunks. Wood often shows deformed and compressed zones, created as a result of overburden pressure during the fossilization process. In addition, crevices and cracks are quite frequent, being filled with thick crystalline quartz, whose genesis is related to subsequent mineralization stages. Trunks show a varied degree of siliceous substance crystallization. Cellular structure is best preserved in pieces penetrated with microcrystalline quartz, whose optic properties are typical of chalcedony (Heflik 1996).

  This text has been prepared on the basis of scientific papers concerning fossilized trees. For technical reasons, the authors have included combined, systematized knowledge about fossils and their origin. At the same time, all substantive conclusions come from the following studies:

o        Bolesław Brzyski, "W sprawie skamieniałych drzew na Roztoczu".

o        Wiesław Heflik, "Badania skamieniałych pni drzewnych z Roztocza".

o        Marzena Kłusek, "Mioceńskie drewno z Roztocza (Polska południowo-wschodnia)".