The Icelandic volcanoes may be divided into three classes: (I) cone-shaped, like Vesuvius, built up of alternate layers of ashes, scoriae and lava; (2) cupola-shaped, with an easy slope and a vast crater opening at the top - these shield-shaped cupolas are composed entirely of layers of lava, and their inclination is seldom steeper than 7°-8°; (3) chains of craters running close alongside a fissure in the ground.
Vesuvius (q.v.), the volcanic forces of which had been slumbering for unknown ages, suddenly burst into violent eruption, which, while it carried devastation all around the beautiful gulf, buried the two cities of Herculaneum and Pompeii under dense beds of cinders and ashes.
According to Lyell, Etna is rather older than Vesuvius - perhaps of the same geological age as the Norwich Crag.
In 1839 he went to Naples and was soon appointed director of the Vesuvius observatory, a post which he held until 1848.
On his pages, close beside the Parthenon, the Sphinx, St Paul's, Etna and Vesuvius, you will find the White Mountains, Monadnock, Agiocochook, Katandin, the pickerelweed in bloom, the wild geese honking through the sky, the chick-a-dee braving the snow, Wall Street and State Street, cotton-mills, railroads and Quincy granite.