A line of craters is seen to the south-west.
At the summit are two deep craters, the southern of which emits steam.
Africa during the Cretaceous period (after the deposition of the Stormberg beds), and drilled these enormous craters through all the later formations.
When, as sometimes happens, two or three of these craters have merged into one, the lake attains a great size.
In the third, after the Campagna, by a great general uplift, had become a land surface, volcanic energy found an outlet in comparatively few large craters, which emitted streams of hard lava as well as fragmentary materials, the latter forming sperone (lapis Gabinus) and peperino (lapis Albanus), while upon one of the former, which runs from the Alban Hills to within 2 m.