2 6o THE POPULAR SCIENCE MONTHLY. 



The presence of graphite, or plumbago, in the Eozoic rocks is by 

 many regarded as a still stronger argument for the former existence 

 of vegetation. As graphite is nearly pure carbon, it is easy to be- 

 lieve that it has accumulated from the remains of plants. Greater 

 changes have been effected in its mass through metamorphism than 

 in the alterations of the ore-beds. No traces of vegetable structure 

 have yet been detected in graphite, so that no evidence as to the na- 

 ture of the earliest plants can be afforded from morphology. 



Nature of the Eozoic Floka. What species of vegetation can 

 we imagine to have existed in these early periods ? Possibly we may 

 derive a hint as to its nature from the general course of plant-devel- 

 opment in later ages, aud assume that there has been a correspondence 

 between the order in which the different classes have appeared and 

 their successive stages of complexity of structure. The simpler forms 

 should appear first ; or, reversing the statement, if we find a succession 

 of all the higher forms of growth in later times, it is reasonable to 

 expect in the still earlier periods larger developments of the inferior 

 cryptogams, such as now play a comparatively insignificant part in 

 the economy of Nature. Their easy decomposition would prevent 

 the preservation of their specific shapes as fossils. 



To particularize, we have among the lower orders of terrestrial 

 vegetation the lichens, by some thought to be the parent of the fungi 

 and algae, since they can be resolved into two different plants, a fun- 

 gus parasitic upon an alga ; the mushrooms, puff-balls, mildews, blight, 

 or fungi ; the hepaticae, and mosses. Of aquatic vegetation there are 

 the numerous protophytes, the diatoms, with their siliceous shells ; 

 the desmids, the coccoliths, with their lenticular calcareous disks ; 

 the nullipores and corallines, making calcareous incrustations; and 

 the great family of Algse, simple, branched, and confluent. These 

 afford us abundant material from which we may reconstruct the 

 Eozoic meadows, forests, and submarine carpets. 



The present system of plants seems to have originated in the Cre- 

 taceous period. The older Mesozoic gives us the cycads and tree- 

 ferns, like those of the Asiatic tropics. The Paleozoic formations 

 furnish a unique assemblage of combined cryptogamous and pheno- 

 gamic nature of types not now existing. Granting that the two 

 divisions of the plant kingdom are of equal importance in the line 

 of development, we find ourselves in Silurian times only half-way 

 back to the starting-point. If the Cambrian should furnish us 

 with representations of the mosses and lichens, we might expect in 

 Eozoic times some of these, together with the protophytes, etc., in 

 order to complete the systematic and orderly development of the 

 plant kingdom in time. Furthermore, the later ages have afforded 

 gigantic representations of the higher orders. Why, then, should not 

 the Eozoic land have had its forests of mushrooms and arborescent 

 lichens; its swamps of diatoms, conferva 3 , the chara? and desmids, 



