Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/351

 Rh Equisetaceæ accompanies their geographical approximation to the Equator, is found in the fossil species of this order to accompany the higher degrees of Antiquity of the strata in which they occur; and this without respect to the latitude, in which these formations may be placed. M. Ad. Brongniart (Prodrome, p. 167) enumerates twelve species of Calamites and two of Equiseta in his list of plants found in strata of the Oarboniferous order.

The family of Ferns, both in the living and fossil Flora, is the most numerous of vascular Cryptogamous plants. Our knowledge of the geographical distribution of existing Ferns, as connected with Temperature, enables us in some degree to appreciate the information to be derived from the character of fossil Ferns, in regard to the early conditions and Climate of our globe.

The total known number of existing species of Ferns is about 1500. These admit of a threefold geographical distribution:

1. Those of the temperate and frigid zone of the northern hemisphere, containing 144 species.

2. Those of the southern temperate zone, including the Cape of Good Hope, parts of South America, and the extra tropical part of New Holland, and New Zealand, 140 species.