Principles of Geology, Vol. 2 of 2: Being an Inquiry How Far the Former Changes of the Earth's Surface Are Referable to Causes Now in Operation (Classic Reprint) - Livres de poche

Excerpt from Principles of Geology, Vol. 2 of 2: Being an Inquiry How Far the Former Changes of the Earth's Surface Are Referable to Causes Now in Operation

But it is still more remarkable, that in the more widely separated parts the ancient continent, notwithstanding the existence of an uninterrupted land communication, the diversity in the specific character of the respective vegetations is almost as striking. Thus there is found one assemblage of species in China, another in the countries bordering the Black Sea and the Caspian, a third in those surrounding the Mediterranean, a fourth in the great platforms of Siberia and Tartary, and so forth.

The distinctness of the groups of indigenous plants, in the same paral lel of latitude, is greatest where continents are disjoined by a wide expanse of ocean. In the northern hemisphere, near the pole, where the extremities of Europe, Asia, and America unite or approach near to one another, a considerable number of the same species of plants are found, common to the three continents. But it has been remarked, that these plants, which are thus so widely diffused in the Arctic regions, are also found in the chain of the Aleutian islands, which stretch almost across from America to Asia, and which may probably have served as the chan nel of communication for the partial blending of the Floras of the adjoin ing regions. It has, indeed, been found to be a general rule, that plants found at two points very remote from each other, occur also in places intermediate.

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