CHAPTER XVII. — SUCCESSION OF VEGETABLE LIFE. 391 



evidence is of the most convincing character, that life — probably 

 both plant and animal — existed in abundance during a consider- 

 able portion of this era. Moreover, we can hardly doubt, that, 

 during this time and the immense unrecorded interval that must 

 have elapsed between it and the time the first rocks of the Paleo- 

 zoic series were deposited, it had developed into numerous, 

 varied and rather complex forms. We ought not to be surprised 

 that, with the dawn of the Paleozoic era, plants and animals — 

 many of them far from being the lowest in the scale — existed in 

 abundance, as shown by their fossil remains. 



Paleozoic Plants. In the very oldest rocks of this era — the 

 Primordial or Cambrian — we find, not only animals in abund- 

 ance, some of them nearly half way up the scale of animal 

 development, but marine algae, some of them of large size and 

 rather complex structure. The forms are not sufficiently well 

 preserved so that we can determine precisely their relationships, 

 but they appear to belong to the Melanophyceae, though the 

 species are all quite different from any at present in existence. 

 The fact that their fossil remains are not nearly so abundant as 

 those of the animals, does not imply that the plants themselves 

 were not abundant. Probably then, as now, animals were 

 dependent on plants for subsistence, and an abundance of the 

 former implies an abundance of the latter, but, as we have already 

 seen, in all geological formations plants are less readily preserved 

 than animals, because fewer of them possess mineralized skele- 

 tons. 



None but marine plants have been preserved to us from this 

 period, and, although it would hardly be fair to conclude from 

 this that no land forms had begun to exist, since these would be 

 less likely to be preserved, they could not yet have attained any 

 considerable development. It is not until we come to the upper 

 formations of the Lower Silurian, that we find distinct traces of 

 plants higher than algae. Here in the shales, particularly of the 

 Cincinnati group, we find numerous sporangia and macrospores 

 of species of Rhizocarpeae, which must have resembled, in habits 

 and structure, our modern Salvinia and Marsilea. These plants 

 must have formed an extensive floating or marsh vegetation. 



In the Upper Silurian, particularly in its later formations, we 

 find the first clear evidence of land vegetation. Among these 



