These hills consist of ragged scoria, elevated 300 to 400 feet above the plain, and are nearly destitute of vegetation.

They are "volcanoes burnt out, and on the lava and ashes and squalid scoria of old eruptions grow the peaceful olive, the cheering vine, and the sustaining corn."

This is owing to the absence of actual lava, the eruptive heat having nearly been sufficient to convert the superincumbent primary and tertiary rocks into a vitreous scoria, having a specific gravity of 3.2, and is highly indestructible in its texture.