The Vistula’s riverbed is a treasure-trove of relics concealed by continually shifting sands and by the turbid river water. So what lies down there, hidden in the Vistula’s depths?

Careful study of river channel hydraulics is helping recover archeological treasures from the bottom of the Vistula River in Warsaw, lost by Swedish looters back in the seventeenth century.

The paper describes the design and construction of the Włocławek water barrage operating on Vistula River for more than 50 years. The construction of the barrage and the damming up of the Vistula River caused changes in the hydraulic and thermal regime of a fifty-kilometre long stretch of the Vistula River, resulting in some ecological changes as well. Some ecologists consider these changes as eminently unfavourable and call for the dismantling of the barrage, but not all experts are of the same opinion as the construction may be regarded as a important technical, economic and social achievement, primarily because of the electricity produced, which is renewable and ecologically clean.

The paper describes a bridge over the Vistula River with two spans of 180 English feet (54.86 metres) in length, constructed in the middle of the 17th century in the city of Torun on the territory of the Polish-Lithuanian Commonwealth. A study on numismatic and iconographic sources as well as city plans and written sources is carried out in the article. The study shows that the Torun Bridge superstructure was made of wood and was based on a cantilever truss (Gerber carrier) solution which had never been applied in Europe before. The two large spans of Torun Bridge were in service between 1632 and 1657. Accord- ing to the author’s research on well-known bridge structures from Europe from the middle of the 17th century, the span of the Torun bridge appears to have been the larger than the other.

We describe a new echinoid assemblage, composed of specimens of Bolbaster sp., Cyclaster danicus (Schlüter, 1897), Diplodetus vistulensis (Kongiel, 1950) and Linthia? sp. in a distinctive phosphatic preservation, from the so-called Greensand, a marly glauconitic sandstone horizon at the base of the Danian succession in the Kazimierz Dolny area (central Poland). This assemblage presumably is of early Danian age, with Cyclaster danicus occurring in the lower Danian of Denmark and southern Sweden. The specimens are preserved as internal moulds, composed of phosphatised glauconitic sandstone, occasionally with some test material adhering. The genesis of these moulds involved the following steps: (1) infilling of tests of dead echinoids with glauconitic sand; (2) penetration of the infills by coelobiotic deposit-feeding organisms that produced burrows along the inner test surface; (3) early-diagenetic cementation of infills by calcium phosphate; and (4) exhumation and intraformational reworking of specimens, leading to abrasion, fragmentation and loss of test material in some individuals. Co-occurring are unphosphatised moulds of Echinocorys ex gr. depressa (von Eichwald, 1866) and Pseudogibbaster cf. depressus (Kongiel in Kongiel and Matwiejewówna, 1937), which may represent a younger (middle to late Danian) assemblage. Additionally, the presence of derived late Maastrichtian echinoids, e.g., Temnocidaris (Stereocidaris) ex gr. herthae (Schlüter, 1892), Pleurosalenia bonissenti (Cotteau, 1866) and Hemicara pomeranum Schlüter, 1902, is confirmed for the Greensand, based on new material and re- examination of previously recorded specimens. In summary, members of three echinoid assemblages of different age and preservation occur together in the Greensand. Our results are compatible with former interpretations of this unit as a condensed, transgressive lag with mixed faunas of different age and provenance. However, they are incompatible with the hypothesis that phosphatised Danian fossils preserved in the Greensand are derived from a facies equivalent, now gone, of the lower Danian Cerithium Limestone in eastern Denmark, because all moulds are composed of phosphatised glauconitic sandstone that is utterly different from the calcareous dinocyst-dominated, fine crystalline matrix of the Cerithium Limestone.