Five million years ago, in the geological period known as Pliocene, clays and sands settled at the bottom of the sea, in that "golfo padano" (Padano Gulf) that at the time covered most of the Italian Northern regions. For thousands of years layers of detritus settled one over the other, enclosing the remains of the creatures living in that ancient sea, that now silently witness of remote times. The calanques around Castell’arquato offer generous evidence of this process.
The hills around Castell'Arquato grew on the sediment that settled over a period ranging from 5 to 1 million years ago, in a tract of sea once communicating with the Adriatic Sea. The calanques located between the streams Chero, Arda and Stirone are rich in the remains of the ancient inhabitants of this sea:molluscs, sea urchins, corals, even whales. Most of the eastern side of Piacenza province is so rich in such fossiles that a geological plan of the Pliocene, the last period of the Tertiary, is known as “Placentianum”, of which the most typical example is the area of Castell’arquato. The geological museum has been open in Castell’arquto since the first 20 years of the 20th century, inside the 16th century restored Ospedale di Santo Spirito. Such edifice is very important not only from the architectural point of view, but also from the urbanistic point of view, because it is the only example in Castell’arquato of portico connected to a street.
The collections in the geological museum are divided into two main categories, the paleonthological and stone collections. As to the fossiles, they are also divided into five sections, plus a section dedicated to the present malacology.
The collection of molluscs from Piacenza’s Pliocene is composed by thousands of pieces concerning 372 entities, divided into: Bivalvian Class (145 species), Gasteropod Class (224 species), Scaphopod Class (2 species), Amphineura class (1 species); the Invertebrates collection is composed by Porifers, Brachiopod celenterates, Echinoderms and Arthropods found in Pliocene territories in the Province of Piacenza (among which a big, wonderful, perfectly preserved crab); the Vertebrates collection is divided into three sub-sections: shark teeth (showing the existence of much bigger sharks than the present ones), whales (the most important collection among those preserved in the museum, with remains of dolphins and whales) and quaternary flooding fauna found in the Province Piacenza, near the river Po (rich in remains of Bison, Elephas, Bos, Cervus, Equus).
In the central hall of the museum there is a gigantic wooden sculture made by Giorgio Rastelli, that shows the visitor the effective dimensions of an acutorostrata whale, typical specimen of the sea fauna that used to dwell in the sea covering PADANA VALLEY up to 1 million and a half years ago.
The vegetables section displays impressions of leaves and and of several fossile pine cones than maintained their original shape.
There are also some finds coming from Brazil, Russia, France, the USA, New Zealand and Australia and a section of the museum (presently under construction) dedicated to present malachology.
The section dedicated to Minerals (also under construction) is divided according to the chemical characteristics of the most common minerals depending on their class: native elements, sulphurs and similar compounds, sulphur salts, aloids, oxides and hydroxides, oxisalts, salts deriving from organic acids, fossile carbon and hydrocarbons; the stones section includes sedimentary and metamorphic magmatic rocks, namely litotypes typical of the Apennine and its minerals.
Visitors can also admire photographic plates and glass slides belonging to the historical collection of Odoardo Bagatti, taken at the beginning of the 20th century, historically and scientifically remarkable. Furthermore, there are some very interesting slides taken during recent expeditions abroad (Ladakh, Urals and Tibet).