106 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



Conclusion. 



In the course of the preceding pages, I have endeavored to notice points 

 of geological and botanical interest as they occurred ; and it will now be 

 necessary only to mention a few leading results, as to the Devonian Flora, 

 which may be deduced from the observations above recorded. 



1. In its general character the Devonian Flora resembles that of the 

 Carboniferous period, in the prevalence of Gymnosperms and Cryptogams ; 

 and, with few exceptions, the generic types of the two periods are the same. 

 Of thirty-two genera to which the species described in this paper belong, 

 only six can be regarded as peculiar to the Devonian period. Some genera 

 are, however, relatively much better represented in the Devonian than in 

 the Carboniferous deposits, and several Carboniferous genera are wanting 

 in the Devonian. 



2. Some species, which appear early in the Devonian period, continue to 

 its close without entering the Carboniferous ; and the great majority of the 

 species, even of the Upper Devonian, do not reappear in the Carboniferous 

 period ; but a few species extend from the Upper Devonian into the Lower 

 Carboniferous, and thus establish a real passage from the earlier to the 

 later flora. The connexion thus established between the Upper Devonian 

 and the Lower Carboniferous is much less intimate than that which subsists 

 between the latter and the true Coal measures. Another way of stating this 

 is, that there is a constant gain in number of genera and species from the 

 Lower to the Upper Devonian, but that at the close of the Devonian many 

 species and some genera disappear. In the Lower Carboniferous the flora is 

 again poor, though retaining some of the Devonian species ; and it goes on 

 increasing up to the period of the Middle Coal measures, and this by the 

 addition of species quite distinct from those of the Devonian period. 



3. A large part of the difference between the Devonian and Carboniferous 

 floras is probably related to different geographical conditions. The wide 

 swampy flats of the Coal period do not seem to have existed in the Devonian 

 era : the land was probably less extensive, and more of an upland charac- 

 ter. On the other hand, moreover, it is to be observed that, when in the 

 Middle Devonian we find beds similar to the underclays of the Coal mea- 

 sures, they are filled, not with Stigmaria, but with rhizomes of PsiLO- 

 PHYTON ; and it is only in the Upper Devonian that we find such stations 

 occupied, as in the Coal measures, by Sigillaria and Calamites. 



4. Though the area to which this paper relates is probably equal to any 

 other in the world in the richness of its Devonian flora, still it is apparent 

 that the conditions were less favorable to the preservation than those of 

 the Coal period. The facts that so large a portion of the plants occur in 

 marine beds, and that so many stipes of Ferns occur in deposits that have 

 afforded no perfect fronds, show that our knowledge of the Devonain flora 

 is relatively far less complete than our knowledge of that of the Coal 

 formation. 



