I860.] KIRKBT PERMIAN FOSSILS. 417 



that no species ranges beyond its own system of strata — beyond the 

 system in which it first appears*. But if there be any veracity in 

 palaeontology, it establishes the fact that species are not confined to 

 systems of strataf. So, if we even assume that the Permian rocks 

 form as sound a system as the Silurian, there are still no reasons for 

 denying upon principle the identifications made. The rules applied 

 to the determination of these species are those which are used in the 

 determination of species belonging to one system. The same prin- 

 ciples which are followed in resolving a fauna or flora into species 

 ought to guide palaeontologists in their more comprehensive studies 

 of the life-groups of adjoining systems; and these I believe to be 

 the principles which have controlled the decisions of Messrs. David- 

 son, Howse, and Jones in the determination of these recurrent spe- 

 cies. Of course the possibility of error is not denied ; but so far as 

 the existing materials supply information, their conclusions appear 

 to be legitimate, and the only ones at which they could philosophi- 

 cally arrive. 



From the preceding list of Carboniferous species found also in the 

 Permian strata of Durham, we are able to see at a glance the specific 

 relationship (so far as at present known) which exists between the 

 life-groups of the later palaeozoic periods. The generic affinity of 

 these groups has long been noticed. The latter feature, and other 

 apparent indications of the absenco of a systematic difference, have 

 originated a proposal that the Permian strata should be included in 

 the Carboniferous system ; and it is not to be denied that the exist- 

 ence of so many Carboniferous recurrents in the Permian fauna and 

 flora lends support to the suggestion. In admitting thus much, I 

 have no wish to abandon the term ''Permian" as the distinctive title 

 of those rocks which now rank under that name ; but I certainly do 

 doubt whether they ought to be classed as a distinct system. 



There appears to be a general want of importance about the 

 Permian rocks as a group, that is opposed to their classification as 

 a separate system. They possess not the vertical range of other 

 systems df strata. Their life-groups are chiefly based upon Carboni- 

 ferous types; and the development of species is exceedingly meagre 

 compared with Bpecies-development in other system-. Consequently 

 there appear to be no reasons for considering thai they represent a 

 period of ancient time that possesses anything like equivalency of 

 value to the periods which other palaeozoic systems apparently indi- 

 cate. It is true, certainly, that the hulk of the Permian species arc 

 distinct ; but Lt is just as true that L5 recurrent Carboniferous species, 

 in the comparatively small fauna and flora of Britain, form a much 

 greater percentage than recurrent species usually occupy in the faunas 

 and flora) of other systems j indeed the percentage is much greater 



than that which obtains in sonic of the subdivisions of the Silurian 



* Sec Bigsln on Pala-ozoic Rucks of NYw York, in Quart. Journ. (Vol. Soo. 

 vol. w. p. 289, where Angelin, Piabet, D'Orbigny, and Agajwia arc quoted u being 



of tins opinion. 



t Sec some interest in;.' remarks on recurrency hv Dr. i>k'-l>\ in Quart. Journ. 

 Gcol. Soo. vol. xv. p. 288-292, 



