Following the walk between Varazze and Cogoleto you come across two types of rock locally called “gianchi” and “neigri”. Among the tunnels and bays along this stretch, which corresponds to the former railway track, you can discover the traces of ancient sea levels that were higher than the current one. The first rocks you come across are metamorphic gabbro (metagabbro) which are light in colour, tending towards yellowish tones if altered on the surface. In order to discover the minerals composing the rock, you need to move out onto one of the first promontories and look at the lighter parts of the outcrops. Looking at them up close, you can see the green-blue crystals, the pyroxenites, immersed in a whitish matrix: microcrystals of plagioclase. The same elements can be seen in the white pebbles of the small beaches between the promontories.
Following the trail for roughly 1,300 metres and going beyond the wide “Baia dei Corvi”, you meet another type of rock. This is serpentinite rock, dark in colour, black with greenish tones, which abundantly crops up along this stretch of the coast. It is not always easy to distinguish the colours of the minerals contained in the rock. They seem an indistinguishable mix of dark green (serpentine) and black (magnetite). Less commonly you find large crystals of pyroxene. This rock is rich in iron and manganese and originates from the ancient Tethys oceanic crust, deriving from the transformation of peridotite rock where almost all the minerals were transformed into serpentinite.