Ansariya, which presently springs up into a high chain of Jurassic limestone with basaltic intrusions, whose peaks rise to 10,000 ft.
They are accompanied by intrusions of diabase and gabbro, and they are sometimes folded, sometimes but little disturbed.
Similar granitic intrusions occurred in New South Wales and Queensland, and built up a mountain chain, which ran north and south across the continent; its worn-down stumps now form the east Australian highlands.
The earlier supporters of the organic theory held that it was a product of the natural distillation of coal or carbonaceous matter; but though in a few instances volcanic intrusions appear to have converted coal or allied substances into oil, it seems that terrestrial vegetation does not generally give rise to petroleum.
In northern Africa a continuous sequence of volcanic events has taken place from Eocene times to latest Tertiary; but in South Africa it is doubtful if there have been any intrusions later then Cretaceous.