126 



REPORT — 1861. 



one are common to both: hence twelve are peculiar to the first, and thirteen to the 

 last area. 



The forty-six genera may be divided into two groups : namely, Ist, those charac- 

 terized by a considerable maxunum specific variety or development before or after 

 Petherwin and Barnstaple times ; and 2nd, those that are not thus distinguished. 



The first of these groups (which alone we have to consider here) contains thirty- 

 one genera, of which six may be said to belong to the past, and twenty-five to the 

 future ; the age of Pethei-win and Barnstaple being the chronological stand-point. 



The " futm'e " division (the only one sufficiently nmnerous to be of service in 

 this inquiry) consists of two series : namely, 1st, those genera which are equally 

 represented in the two sets of beds ; and, 2nd, those that are not, -Evidently the 

 latter series alone can supply information on tlie present question. It is made up 

 of the fifteen genera named in the following Table, in which the columns headed 

 P. B. C. exhibit the number of species belonging to each genus which occur in 

 the Petherwin, Barnstaple, and British Carboniferous beds respectively. 



From the Table we leam that nine of these genera are found in Bamstaple and 

 not in Petherwin, or are more largely represented in the former than in the latter ; 

 and that nineteen species represent the ten genera found in the former area, whilst 

 no more than ten the eight genera of the latter. Hence the geucrn, like the 

 species, suggest that the Barnstaple beds are somewhat more modem than those 

 of Pethei"win. 



AVe are prepared, by even a slight acquaintance with the geographical distribu- 

 tion of existing organisms, to find that deposits strictly contemporary, lithologically 

 similar, and closely comiected geographically, have certain fossils peculiar to each. 

 But unless we recognize time as a factor, it will be difficult to explam the facts that 

 Pethei-win and Barnstaple have together yielded as many as 131 species of fossils, 

 yet have no more than seventeen in common ; that the "fossils belong to forty-six 

 genera, of which twenty-five are restricted to one or other of the two areas, having 

 amongst them the rich genus Clymeiiia with its eleven species, all closely con- 

 fined, in Britain, to Petherwin, yet occmTing in Continental Europe; that the 

 remaining twenty-one genera are represented, in the two areas, by eighty-six 

 species ; but the representatives are rarely identical in the two sets of beds, the 

 peculiar being to the common as 69 to 17, that is about 4 to 1. Contend that these 

 beds are strictly contemporary, and the facts remain to puzzle ; grant but the 

 lapse of time, and, tit least, part of the difficulty disappears, and thereby fmnishes 

 an argimient in favour of the opiaion now advocated. 



Eetuming for a moment to Tables II. and III., it will be seen that the Bam- 

 staple beds have a smaller number of species in common with the Lower Deronian 



