In the Viñales area, outcrops of rounded, often elliptical, rocks are found in numerous locations. They can be between 10 and 50 cm in diameter. The local people call them "cheeses" because of their resemblance to large round cheeses. These structures may contain fossil remains, both in the core and on the outside. The most abundant are ammonites, but reptile and fish remains have also been found. They are Jurassic in age, generally from the Oxfordian (between 155 and 160 Ma). These rocks are actually calcium carbonate concretions that form during sediment diagenesis, that is, the transformation of soft sediments from the seafloor into rocks. They form in marine basins where clays, materials with limited permeability, are abundant. When clayey sediments compact, permeability decreases vertically, giving rise to calcium carbonate concretions, forming spheres that gradually increase in volume and deform under the weight of the sediment, creating elliptical shapes. The presence of phosphates and bacteria involved in the decomposition of organic matter facilitate the precipitation of these carbonates. For this reason, fossils are frequently found inside the "cheese."