Let us see now the reason behind the change of direction. As we said before, the evolution of the cave was possible because of a series of inverted faults and over sliding, as well as the Mount Acqua quartzite and calcareous rocks. The abundant presence of quartzite rocks along the main structural alignment is linked to the intense tectonic movements of the area around San Giovanni’s cave.
One of these quartzite bodies is the left wall. Quartzite is one of the most physically durable and chemically resistant rocks in nature, making it not subject to Karst erosion, features that characterised the geologic evolution of the southern side of the cave. The river, on its course, found the hard rocky body, and literally changed is course with a sharp 150 degrees turn to skip the obstacle, to take back its original direction North- South once overcome the obstacle. In the last part of the gallery. Looking on the west, we spot several formations, making us suppose another ramification once existed, now closed by deposits.
In front of us we can see a huge stalagmite formation that is been sectioned partially by erosion and partially man made during the road construction. This body is the remnants of what once was the cave’s pavement covering the whole length of the cave. Following the increased volume of water flowing from the river, much of it is been desmanteled in its orginal central portion.
A more careful observation of the section shows periods of higher formation followed by period of deposition of material or erosion and dissolution. It is possible to see a rimstone (gours) containing ten pisolites, evidence of secondary mineralization of the rocks yet to be understood.
