Data Mining: Vismara (cont)

On the geology of the area:

• The tufa of the Monteverde region was 'celebrated' and quarried for construction material, leading to a landslide in the area.
  
• The catacombs were excavated in the less compact upper strata.
  
• Scholar De Angelis d'Ossat conducted a study of the geology of the area published in 1939 (La geologia delle catacombe romane, in Roma Sotterranea Cristiana III, Cita del Vaticano).
  
• De Angelis d'Ossat divides the catacombs in the following way (from bottom to top; pp23-25 and fig. 8 of the publication):
• ---30m-10m : tufa of lithoid construction (tufo litoide da costruzione) which was partially visible in the quarries.
• ---10m-7m: homogenous, fine grained and with minute stratification, easily fractured.
  
• ---7m-6m: coarse black volcanic debris with detritis, of non-homogenous and permeable granular volcanic tufa. It was in this layer that the majority of catacombs were dug.
  
• ---6m and above: sandy loam and limestone layer.