PALEOZOIC ROCKS AND EttA. 28? 



Physical Geography. The land during early Devo- 

 nian times was the Archaean area, increased by the addi- 

 tion of the Cambrian and Silurian area, the Devonian area 

 being then of course sea-bottom. In the middle of the 

 Devonian Sea there was a large island of Silurian rocks 

 occupying what is now mid- Ohio and running down 

 through mid-Tennessee. At the end of the Devonian, 

 the Devonian area was exposed as land and added to that 

 previously existing. 



Subdivisions. The American Devonian is subdivided 

 into at least four groups of strata representing four periods, 

 as shown in the schedule. We shall, however, neglect 

 these subdivisions in our general account of the life- 

 system : 



4. Chemung period. 

 3. Hamilton period. 

 2. Corniferous period. 

 1. Oriskany. 



Life-System of Devonian. Plants. 



In Silurian times, with the exception of a very few 

 small vascular cryptogams allied to club-moss, we found 

 nothing higher than f ucoids. In addition to these, now, 

 for the first time, land-plants become conspicuous. Here, 

 for the first time, we have a true forest vegetation. The 

 character of the trees of this first forest is a question of 

 the highest interest. The Devonian forests consisted of 

 the highest cryptogams, vascular cryptogams, and the 

 lowest phenogams, Oymnosperms. More explicitly, there 

 were Ferns, Lepidodendrids, and Sigillarids (gigantic 

 club-mosses), and Calamites (gigantic Equisetce) among 

 vascular cryptogams : and Conifers allied to the yews 

 among gymnospermous phenogams. 



We shall not describe these now, since they are all 

 much more abundantly represented in the Carboniferous. 



