144 LIFE ON THE EARTH. 



the Coal-formation. Ferns are usually in fragments, 

 distributed by water on the successive surfaces of 

 deposition. It can seldom be ascertained whether 

 they belonged to arborescent or repent kinds, but 

 two or three species of the former division under 

 the title of Caulopteris are recognized in the Coal- 

 measures. The great abundance of Ferns is a fur- 

 ther and good argument for great warmth and damp- 

 ness. If Lepidodendra belong to the natural order 

 of Lycopodiaceee, their extraordinary size may be 

 held to demand the extreme of the conditions fa- 

 vourable to that race, heat and moisture; if they 

 include strong analogies to Araucarise, that is an 

 indication in the same direction. Sigillarise, now 

 commonly placed among the Gymnospermous Pha- 

 nerogamia, near Cycadacese, have also been thought 

 allied to Cacteaceae, and to Tree-ferns, and thus 

 follow on the same side as their companions the 

 Lepidodendra. 



Calamites, no longer referred to Equisetacese, 

 but with Asterophyllites classed among Coniferce, 

 give no independent testimony to climate ; but a few 

 Palms (Flabellaria, Palmacites, Trigonocarpum), and 

 Musacese (Musocarpum), concur with the Tree-ferns 

 in requiring for the low shores of early time, where 

 now extend the coal-deposits of America and Europe, 

 a mean temperature of 64, which is 16 above that 



