The da Vinci family had no properties in the area of Collegonzi, but Leonardo possessed an excellent knowledge of this part of Montalbano. This is demonstrated by his observations on the origin of the geological stratifications of the gorge of La Gonfolina and his extensive reflections on the presence of fossils of marine origin in the vicinity of the Collegonzi, the famous "nichi" (fossil shells) recalled in the Leonardo codices. The broad passages dedicated to the subject, concentrated on various folios of the Codex Leicester, revolve substantially around the theory that the different geological layers he observed in the Arno Valley were due to the action of the ancient sea that, in most remote eras, reached La Golfolina, where it received the waters of the Arno. According to Leonardo, the movement of the sea waters shaped the lithic material that the rivers discharged into the ancient sea, giving rise to geological layers of different composition, from coarsest to finest: the "ghiara minuta" (minute gravel), the "rena" (sand), and finally the "fango" (mud). The retreating of the waters of the Pliocene sea must have placed the coarser and heavier deposits along the ancient shores further upstream, and the finer and lighter ones, along the banks further downstream. Leonardo observed and explained in this way the presence of "sassi grandissimi” (very large stones) and "ghiara" (gravel) around Montelupo and Capraia, the "rena" (sand), even finer, toward Castelfiorentino, and finally the "fango" (mud), the finest and lightest, at Collegonzi (Codex Leicester, ff. 6A-31v; 8B-8v). And here is the point of insertion of Leonardo’s theory of the "nichi" of Collegonzi, the fossil shells he saw in great quantity within the "mud" deposits, that is, the thinner geological layers that once formed the bottom of the Pliocene sea. The rising of the sea floor, followed by its subsequent drainage, had, for Leonardo, given rise to that particular formation composed of alternating layers of bluish mud and "nichi," which he had especially observed around Collegonzi. Leonardo writes: "the mud, in which the shells lived, which rose gradually by degrees, in accordance as the floods of the turbid Arno poured into that sea, from time to time raising the bottom of the sea, which by degrees produced these shells, as is shown in the cut bank at Colle Gonzoli [...]" (Codex Leicester, ff. 8B-8v). At the foot of Collegonzi the erosive action of the Arno must have exposed, according to him, a geological section, the "cut bank of Colle Gonzi, which bank is undone by the River Arno, which consumes at its base: within which cut bank you may clearly see the aforesaid degrees of shells in bluish mud, and there may be found various things from the sea [...] "(Codex Leicester, ff. 8B-8v). Up until a few years ago, there was a clay quarry at Collegonzi, with the Pliocene stratification containing the levels of seashells representing the coastal marine environment observed and described by Leonardo.