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America, where these formations are mutually unconformable, 

 there is, of course, less room for doubt than in Ireland and in 

 Western America, where they are stratigraphically continuous. 

 Still, in passing from the one to the other, the species are for 

 the most part different, and new generic forms are met with, 

 and, as I have elsewhere shown, the physical conditions of the 

 two periods were essentially different.* 



It is, however, to b' bserved that since, as Stur and others 

 have shown, C<(lumitc.s nidudns and other forms distinctively 

 Devonian in Americ.i, occur in Europe in the Lower Carboni- 

 ferous, it is not unlikely that the Devonian Flora, like that of 

 the Tertiary, appeared earlier in America. It is also probable, 

 as I have shown in the Reports already referred to, that it ap- 

 peared earlier in the Arctic than in the Temperate zone. Hence 

 an Arctic or American Flora, really Devonian, may readily be 

 mistaken for Lower Carboniferous by a botan'st basing his cal- 

 culations on the fossils of temperate Europe. Even in America 

 itself, it would appear from recent discoveries in Virginia and 

 Ohio, that certain Devonian forms lingered longer in those 

 regions than further to the North-east ;f and it would not be 

 surprising if similar plants occurred in later beds in Devonshire 

 or in the South of Europe than in Scotland. Still, these facts, 

 properly understood, do not invalidate the evidence of fossil 

 plants as to geological age, though errors arising from the neglect 

 of them are still current. 



I trust that Scottish workers in this interestinii; though diffi- 

 cult branch of investigation, will be encouragod by the success 

 they have already attained to still more diligent seaich. in col- 

 lecting, the smallest and mo.st obscure fragments should not be 

 neglected. Such specimens, when placed in due relation to 

 others previously obtained, may reveal the most important truths ; 

 or if by themselves unintelligible, may be rendered valuable 

 by subsequent discoveries. The greatest care should be taken 

 to rescue every portion of the specimens found, and to keep 

 together those that belong to the same plant ; and every fragment 

 likely to show microscopic structure should be carefully preserved. 

 Painstaking work of this kind will be sure to be rewarded by 

 important discoveries ; and I know by long experience that none 

 other is likely to be successful, 



* Reports on Devonian Plants and Lower Carboniferous Plants of 

 Canada. 



t Andrews, Pala3ontology of Ohio, Vol. II. Meek, Fossil Plants 

 from Western Virginia, Philos (Society, Washington, IS?.*), 



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