The main aim of the excavations at mine No.1 of the Defensola A was to complete the trench in the knapping area of chamber A3 by reaching the rock floor. A secondary objective was the search for charcoal samples in the lower floor immediately below the knapping area.
The excavation, limited to only three squares, was completed. It investigated the lowest part of the fill, below deposit 10A-F, constituted by a second sequence of artificial cuts still within stratigraphic unit 10 (10G-O) in square A6 and in part in square B6, and by a limestone plate with very discontinuous brown earthy elements (alfa) in the other part of B6 and the whole of C6. The two sequences were separated by a diaphragm formed from the mine’s rocky floor. The external sequence (10G-O) was constituted by an imposing breccia with worked limestone and silica elements. Its excavation, necessitated the use of metal chisels, however, most of the worked pieces were given coordinates. Below sequence 10G-O, without an apparent break in continuity, was another limestone breccia poor in worked silica elements (US11). This was interpreted as detritus from quarrying activities in this part of the mine, before the creation of the knapping area. In the sequence situated to the interior with respect to the diaphragm, deposit 10A-F overlay the alfa plate. Below, only in correspondence with section XVIII, a sediment appeared with non concretionary gravel and poor in evidence of the lithic industry, whose stratigraphic collocation with respect to the sequence in square A6 remains to be resolved (11?). Finally, the mine’s rocky floor appeared in the trench, its morphology somewhat uneven, in particular on the left side of the trench, towards section XVIII. Its height with respect to the ceiling in some points was circa one metre.
The series corresponding to the accumulation of materials produced by the knapping activity was substantially constituted, at least on the basis of the deep excavation in squares A6, B6 and C6, by three broad horizons. Starting at the top, the first was made up of an accumulation of knapped stone, completely loose and of variable thickness, excavated with eight overlying artificial surfaces, representing the last episode of débitage. A second horizon (US9) followed, constituted this time by a light brown earthy sediment and abundant lithic industry especially in the mid to lower part (US9 earthy/lithic), attributable to a second episode of débitage, dated to 6551+/-40 BP. The presence of earthy sediment suggested a communication with the exterior of chamber A3. Lastly, a third horizon was represented by a breccia (US10) incorporating limestone gravel and above all lithic industry deriving from a third episode of débitage. The concretion, which effected the entire stratigraphic unit although in a diverse ways, could be linked to the opening, no longer visible as obstructed by detritus, present on the left side of chamber A3, precisely where a stalagmatic flow is now visible which incorporates part of the débitage, probably that of the third horizon. A recent radiometric dating on a charcoal sample from the base of layer 10 (10 O) places the beginning of the knapping activity to 6741+/-50 BP, in calibrated chronology 2s between 5730 and 5560 B.C.
The conclusion of the investigation in the knapping area sees a temporary end to the research on the upper level of the Defensola mine, which has lasted for almost twenty-five years. The exploration of its interior stopped, as is known, at the part that could be physically reached.
The lower level remains completely unexplored. This could only be reached for a brief stretch from the shaft communicating with the upper level and no charcoal samples for radiometric dating were found. Exploration of the lower, certainly earlier, level remains the main objective for a future research programme.
