THE PRIMARY EPOCH. II 



the forest vegetation of the mainland, which was then 

 utterly wanting. All the animals, also, whose remains have 

 been found in archilithic strata, like the plants, lived in 

 water. Only Crustacea are met with among the animals 

 with articulated feet, as yet no spiders and no insects. Of 

 vertebrate animals, only a very few remains of fishes are 

 known as having been found in the most recent of all 

 primordial strata, in the upper Silurian. But the headless 

 vertebrate animals, which we call skull-less, or Acrania, and 

 out of which fishes must have been developed, we suppose 

 to have lived in great numbers during the primordial epoch. 

 Hence we may call it after the Acrania as well as after the 

 Tangles. 



The primary epoch, or the era of Fern Forests, the second 

 main division of the organic history of the earth, which is 

 also called the palseolithic or palaeozoic period, lasted from 

 the end of the Silurian formation of strata to the end of the 

 Permian formation. This epoch was also of very long dura- 

 tion, and again falls into three shorter periods, during which 

 three great systems of strata were deposited, namely, first, 

 the Devonian system, or the old red sandstone ; upon that, 

 the Carhoniferous, or coal system; and upon this, the 

 Permian system. The average thickness of these three 

 systems taken together may amount to about 42,000 feet, 

 from which we may infer the immense length of time 

 requisite for their formation. 



The Devonian and Permian formations are especially rich 

 in remains of fishes, of primeval fish as well as enamelled 

 fish (Ganoids), but the bony fish (Teleostei) are absent from 

 the strata of the primary epoch. In coal are found the 

 most ancient remains of animals living on land, both of arti- 



