Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/350

 346 that are preserved in the Strata of the Carboniferous Order, beginning with those which are common both to the ancient and existing states of Vegetable Life.

Among existing vegetables, the Equisetaceæ are well known in this climate in the common Horse-tail of our swamps and ditches. The extent of this family reaches from Lapland to the Torrid Zone, its species are most abundant in the temperate zone, decrease in size and number as we approach the regions of cold, and arrive at their greatest magnitude in the warm and humid regions of the Tropics, where their numbers are few.

M. Ad. Brongriart has divided fossil Equisetaceæ into two Genera; the one exhibits the characters of living Equiseta, and is of rare occurrence in a fossil state; the other is very abundant, and presents forms that differ materially from them, and often attain a size unknown among living Equisetaceæ; these have been arranged under the distinct genus Calamites, I they abound universally in the most ancient Coal formation, occur but sparingly in the lower strata of the Secondary series, and are entirely wanting in the Tertiary formations, and also on the actual surface of the earth.

The same increased development of size, which in recent