148 THE GEOLOGICAL HISTORY OP PLANTS. 



flora from that of the Mesozoic, in the same manner that 

 Eamsay has supposed a similar period of cold to have done 

 north of the equator. This would imply a very great 

 change of climate, since we have evidence of the exten- 

 sion of the Lower Carboniferous flora at least as far 

 north as Spitzbergen. The upper coal-formation we 

 cannot, however, trace nearly so far north ; so that a 

 gradual refrigeration may have been going on before 

 the Permian. Thus in both hemispheres there was a 

 general similarity in the later Palaeozoic flora, and per- 

 haps similar conditions leading to its extinction and to 

 its replacement by that to be described in the next 

 chapter. 



NOTES TO CHAPTER IV. 

 I. Characters and Classification op Paleozoic Plants. 



In the space available in this work it would be impossible to 

 enter fully into the classification of Pala30zoic plants ; but it may be 

 well to notice some important points for the guidance of those who 

 may desire to collect specimens ; more especially as much uncer- 

 tainty exists as to affinities and very contradictory statements are 

 made. The statements below may be regarded as the results of 

 actual observation and of the study of specimens in situ in the rocks, 

 as well as in the cabinet and under the microscope. 



Gtmnosperme^. 



Family Coniferje; Genus Dadoxylon, Endlicher; Araucaeites, 

 Goeppert ; Aratjcarioxylon, Kraus. 



The trunks of this genus occur from the Middle Devonian to the 

 Permian inclusive, as drift-logs calcified, silicified, or pyritised. The 

 only foliage associated with them is of the type of Walchia and 

 Arauca/rites — viz., slender branches with numerous small spiral acicu- 

 lar leaves. Two of the coal-formation species, D. materiarum and 

 another, had foliage of this type. That of the others is unknown. 

 They are all distinct from the wood of Cordaiies, for which see under 

 that genus. 



