LIFE 367 



comprised in one system, and the Carboniferous and Permian in 

 another ; but the present tendency is in favour of maintaining all 

 six as equal in rank. It must not be supposed that these sys- 

 tems represent equal spaces of time as measured by the thickness 

 of rocks, or equal geographical extent ; on the contrary, they are 

 very unequal in both these respects. The classification means 

 that the six systems, or periods, stand for approximately equiva- 

 lent changes in the character of the animals and plants. 



Palaeozoic Life possesses an individuality not less distinctly 

 marked than that of the group of strata, which demarcates it 

 very sharply from the life of succeeding periods, and gives a cer- 

 tain unity of character to the successive assemblages of plants 

 {floras') and of animals {faunas). The era is remarkable both 

 for what it possesses and what it lacks. Among plants, the vege- 

 tation is made up principally of Cryptogams, seaweeds, ferns, 

 club-mosses, and horsetails. Especially characteristic are the 

 gigantic, tree-like club-mosses and horsetails, which are now 

 represented only by very small, herbaceous forms. The only 

 flowering plants known are the Gymnosperms, the Cycads and 

 their allies ; no Angiosperms have been discovered. Palaeozoic 

 forests must have been singularly gloomy and monotonous, lack- 

 ing entirely the bright flowers and changing foliage of later periods. 



The Palaeozoic fauna is largely made up of marine inverte- 

 brates, in the earlier periods entirely so, i.e. so far as we have yet 

 learned, though land life surely began before the oldest records 

 of it yet discovered. Corals, Echinoderms (especially Crinoids, 

 Cystideans, and Blastoids), Brachiopods, Mollusca (particularly 

 the Nautiloid Cephalopods), and the crustacean group of Trilo- 

 bites are the most abundant and characteristic types of animal 

 life. Insects, centipedes, and spiders were common toward the 

 end of the era. Cambrian rocks contain no fossil vertebrates, but 

 they make their appearance in the Silurian, and perhaps earlier. 

 For long ages the only vertebrates were fishes and certain low 

 types allied to the fishes, but at the end of the Devonian and in 

 the Carboniferous appeared the Amphibia, followed in the Permian 

 by true Reptiles. Teleosts, such as make up by far the largest 



