| The peperino, much used at Rome and Naples as a building stone, is a trachyte tuff. |
| The cone itself is evidently composed of similar beds super-imposed, and holding fragments of porphyry and trachyte. |
| Not a single specimen of its trachyte has ever been deposited in a European museum. |
| Some of these are composed of trachyte, others of compact blue basalt with olivine. |
| In the south of the island there are sills and dykes of felsite, quartz-porphyry, rhyolite, trachyte and pitchstone. |
| Pumice and trachyte are the most common rocks around this mountain, and these are augitic or porphyroid. |
