[ 3 ] 



CHAPTER I 



THE GEOLOGICAL AGE OF THE FLORAS 



The question of the Geological age of the floras known from 

 various parts of the world is so vital to the conclusions of this 

 inquiry, that this matter demands special consideration at the 

 outset. So far as we are aware, no one has ever disputed the age 

 of the various beds from which these fossils are derived, with 

 a view to proving them to be younger than Devonian times. 

 Attempts have, it is true, been made in some cases to establish 

 a pre-Devonian age, particularly in Bohemia and Germany. 

 These views are however, we believe, now almost entirely 

 abandoned, and so they need not detain us here. In the great 

 majority of cases, there is stratigraphical or zoological evidence, 

 from the associated sediments, of undoubted Devonian age. 

 Further, as Nathorst and Halle have recently pointed out, the 

 De\'onian flora is now so well known, that the age can usually 

 be established by a consideration of the plant remains alone. 



Such doubt on the geological side as may exist, relates not to 

 the question of age, but of horizon. This is often a more serious 

 difficulty, but it is not one Avhich is of first importance from 

 the botanical standpoint. We propose, however, to review the 

 evidence as to the horizon, wdiether Lower, Middle, or Upper 

 Devonian, of our more important Devonian floras, beginning 

 with that of Scotland. 



Scotland. The Old Red Sandstone flora of Scotland has now 

 become of particular importance in view of the recent researches 

 on Rhynia and Parka to which we have drawn attention. The 

 former comes either from the Middle Old Red or from a lower 

 horizon. The latter is only known from the Lower Old Red, so 

 far as Devonian rocks are concerned. 



The sub-division of the Scottish Old Red Sandstone has been 

 a matter of some difference of opinion, but the modern view is 

 that the original threefold classification proposed by Murchison 

 in 1859 is correct. Murchison distinguished an Upper, Middle, 

 and Lower division, each characterised by a pecvdiar fish faima. 

 This classification is now accepted by the Geological Survey of 



I — 2 



