3. By the inspection of territories disturbed by the uprising of mountains, and beds which form long chains, one can determine their geological age. By the geological age of mountains, it is not necessary that we understand it as the number of the years of their existence, but the period during which they have been formed, and consequently their relative antiquity. It would be an error to suppose that this antiquity is by reason of their elevation, or of their exclusively granite nature, considering that the mass of granite, while being thrown up, can have perforated and separated the superposed beds.
It has thus been ascertained by observation that the mountains of Vosges, of Bretagne, and of the Côte d’Or, in France, which are not very high, belong to the ancient formations. They date from the transition period, and are anterior to the coal deposits. The Jura has been formed near the middle of the secondary period. It is contemporary with gigantic reptiles. The Pyrenees have been formed later, - at the commencement of the tertiary period. The Mont Blanc, and the group of Western Alps, are posterior to the Pyrenees, and date from the middle of the tertiary period. The Eastern Alps, which comprise the mountains of the Tyrol, are more recent still; for they were not formed until the end of the tertiary period. Some mountains of Asia are posterior to or contemporary with the deluge period.
These uprisings must have been due to great local perturbations and inundations, - greater or less according to the extent of the displacement of waters, and the interruptions and changes of course of rivers. *
* The last century offers a remarkable example of a phenomenon of this kind. Six days journey from the city of Mexico was found in 1759 a fertile and well-cultivated country, where grew an abundance of rice, corn, and bananas. In the month of June frightful earthquakes agitated the soil, and the trembling continued two whole months. In the night of Sept. 28 and 29 the earth experienced a violent commotion; a territory of many miles in extent was slowly raised, and attained a height of five hundred feet upon a surface of thirty square miles. The earth undulated like ocean-waves in a tempest. Millions of hillocks alternately rose and fell. At length a gulf, nearly nine miles in extent opened. From it proceed smoke, fire, burning stones and ashes, which were thrown to a prodigious height. Six mountains rose from this yawning gulf, among which the volcano Jorullo was raised to about five hundred and fifty yards, or thirteen hundred and seventy-five feet, above the former plain. At the moment the earthquake commenced, two rivers, - the Cuitimba and the Rio San Pedro, - flowing behind, inundated the whole plain occupied now by the Jorullo; but a gulf opened, and swallowed them. They reappeared in the west, very far away from their ancient bed. (Louis Figuer: “The Earth before the Deluge,” p.370).