Access to the ditch Anguillaja: parked the vehicle on the edge of the provincial road of Val d’Arni (687 m above sea level), which leads to Castelnuovo Garfagnana, you walk on foot along an old cart track, which opens on the left and descends towards the Dry Tùrrite. After 250 m you reach the watercourse which, as a rule, is completely dry, since it is characterized by a subalveous circulation. After having traveled the arid bottom in a northerly direction, while the river shaft draws a recessed meander, you immediately meet the confluence from the left of the Anguillaja ditch (650 m above sea level), largely modified by the old cuts and the abandoned residues of a Marble quarry. The mining activity also canceled the first ‘potholes’ that existed in the lower part of the same ditch, artificially shaping its bottom and its side walls.
The Anguillaja is an intermittent watercourse on a temporary basis, on the occasion of heavy rains, which presents some remarkable ‘potholes’, described for the first time by Masini (1929). At that time, the last 300 m of the ditch descending from M. Sumbra, showed 13 large cauldron cavities. Their number then decreased due to the destruction produced years ago by the disused quarry of its lower section. The surviving ‘potholes’, now protected by the Regional Park, are easily observable by continuing the short itinerary along the Anguillaja. The ascent of the ditch is relatively easy at the beginning and, the first morphological jump, is overcome thanks to a small iron staircase. This leads to the spectacular succession of three ‘potholes’ of significant proportions, completely carved out of marble (see photo on the side).
Further on, the route requires practice in the use of the double rope and in climbing adherence on rock.
Morphogenesis: the ‘pots of the giants’ often owe their origin to the abrasive action of rotating pebbles. The development requires several coincident conditions, including the swirling movement of the river current and a coherent and homogeneous rocky substrate, such as the marble of M. Sumbra.
The ‘mufflers’ of Anguillaja and Fatonero also seem to refer to this model, as the signs of mechanical erosion on the inner edges of the large cauldron cavity shown on the side would demonstrate.
However, some Authors have hypothesized a genesis of these ‘potholes’ in a forced regime, through subglacial tunnels that were to be located in the southern slope of Sumbra and Fiocca, in correspondence with glaciers or perennial snowfields formed during the last ice age.
For others, chemical dissolution (surface karst) may have initially prepared the cavities, on which the hydrodynamic action then had a prevalent or exclusive reason (Federici et alii, 1981).
A look at the Fatonero ditch, the Fiocca and the Sumbra
From the provincial road of Val d’Arni, 700 m further upstream from the Anguillaja, the Fatonero ditch is easily identifiable, of which the last 400-500 m of stretch can be observed, descending from M. Fiocca. The ‘potholes’ have been numbered decreasing as the ditch goes up: in all they are 21 and the same size as the twin ditch. They too are carved out of marble.
On the way up the M. Fiocca, from the Fatonero ditch, we find, in succession, Marbles, Selciferous Limestones, Diaspri, Selciferous Limestones at Entrochi, Sericitic Schists and Pseudomacigno, with different repetitions due to minor folds. It should also be noted the presence of three tiny klippe of cavernous limestone. M. Sumbra, on the other hand, consists mainly of Marbles and Selciferous Limestones. The southern slopes of these two hills are characterized above all by karst and glacial modeling. The rounded furrows of the south wall of the Sumbra are linked to cryonal processes, due to perennial snowfields or small ephemeral masses of ice.
