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PRE-CARBONIFEROUS PLANTS. 



69 



Coal-formation, though presenting some characteristic differences, more 

 especially in the less extensive prevalence of swampy flats. Con- 

 temporaneously -with the very beginning of these physical changes 

 appeared the Erian Flora. Already, before the close of the Tipper 

 Silurian, the first patches of emerging land must have become clothed 

 with Pailophyton, and by the time of the Middle Devonian the flora 

 of the period had, at least on the Atlantic coast, ' attained to its 

 culminating point. 



At the time when the Erian or Devonian Flora attained to its greatest 

 extension, there must have been in Canada a considerable extent of Lau- 

 rentian and Lower Silurian land. The Adirondack hills were out of the 

 water, and so were the older portions of the Appalachians, and from these 

 there stretched to the East, West and South, considerable tracts of low 

 land ; portions of which were alternately dry and submerged according to 

 the varying level of the continent. Upon these flats, and in part also, 

 probably, on the neighbouring hills, flourished the plants which have been 

 described in the preceding pages, and which appear to have enjoyed 

 climatal and atmospherical conditions similar to those of the Carboniferous 

 period, but with a smaller continental area and greater proportionate 

 irregularity of surface. 



At the close of the Devonian, in the regions lying east of the Appa- 

 lachians, great physical disturbances occurred. The lowest Carbonifer- 

 ous rocks are generally coarse and conglomerated, often interstratified 

 with contemporaneous trap, and rest unconformably on the Devonian. The 

 latter rocks are much altered, and this metamorphosis is connected with 

 the intrusion of great masses and dykes of granite which penetrate the 

 Devonian, and were consolidated before the deposition of the lowest Car- 

 boniferous beds. These disturbances were the prelude to the great 

 change in animal and vegetable life which wo find in the lowest 

 Carboniferous beds, and to the subsidence evidenced by the prevalence 

 of the Lower Carboniferous limestones, which separate as by a great 

 gulf the Lower Carboniferous flora from that of the Middle Coal 

 formation. 



In the east these changes were already in progress in the latter part 

 of the Devonian, as evidenced by the coarse sandstones and conglo- 

 merates of the old red sandstone. In the west they did not occur, or were 

 postponed till after the Carboniferous had begun, since in Ohio we find a 

 gradual passage from the Devonian into the Carboniferous, while a par- 

 tial unconformability occurs between the Lower Carboniferous and the 

 Coal-formation. Even in the west, however, the Devonian Flora disap- 

 pears at the beginning of the Carboniferous period. 



