64 ME. D. DATTES OX THE ECOLOaT OF [vol. Ixxvii, 



The most significant fact that has impressed me in the ex- 

 amination of the different horizons is the sudden disappearance of 

 the Filicales and Pteridosperms, as we ascend the series to the 

 Two-Foot Nine and Pentre Seams, and the prominent appearance 

 of the LycoiDodiales in their place. 



How is it that the Two-Foot Xine Seam only yields 24: specimens 

 of Filicales and Pteridosperms, Avhereas it yields no fewer than 

 935 specimens belonging to the Lycopods r The Pentre Seam, 

 again, produced 551 Filicales and Pteridosperms, but no fewer 

 than 2051 Lycopods. It is very evident that some great physical 

 changes occurred in Two-Foot Xine Seam and Penti-e Seam times, 

 and that the flora must have greatly altered in consequence. 



For some reason or other, the Cordaitales and Equisetales are 

 not so strongly influenced as the Filicales. Pteridosperms. and 

 Lycopodiales by these changes, and it is fair to infer that the three 

 last-mentioned groups were, during life, more sensitive to their 

 surroundings than the first two. 



Possibly it would be well to set forth here the converse evidence 

 of the relative frequency of the Filicales and Pteridosperms in 

 comparison with the Lycopodiales. The evidence found in the 

 Two- Foot Xine and Pentre Seams and in the two succeeding and 

 the two preceding seams, respectively, is very interesting. In the 

 Xine-Foot and Six-Foot Seams the Lycopods number 196 in the 

 former, and 32 in the latter ; whereas the Filicales and Pterido- 

 sperms number 1624 in the Xine-Foot Seam, and 3127 in the 

 Six-Foot Seam. This is a very striking contrast. The Lyco- 

 pods have nearly disappeared in the two seams immediately above 

 the Two-Foot Xine and Pentre Seams ; and the Abergorky Seam, 

 which occurs directly above the last-mentioned seam, only produced 

 9 specimens of these plant-remains. There are no fewer than 

 21 plants representing the Filicales and Pteridosperms in this seam. 

 Again, in the Xo. 3 Ehondda Seam, the Lycopods were represented 

 by only 14 specimens, Avhereas the Filicales and Pteridosperms 

 were represented by 2341 specimens. 



If the plant-bearing sediments on the sea-bottom are a faint 

 reflex of the distribution of the plants covering the land-sui-face 

 from which they were transported, due allowance being made for 

 plants growing near the open seas and deltas, the instances above- 

 mentioned imply the existence of a swampy surface with a flora of 

 Lycopodiales flourishing during the period of the formation of the 

 Two-Foot Xine and Pentre Seams. It will also be noticed that 

 in the seams below and above, ferns and fernhke plants Avere more 

 abundant and the Lycopods scantier, thus showing that the former 

 flourished in profusion as a dry-land flora. 



It is admitted that Equisetales grow in swampy ground and 

 possibly on the slopes fringing the open seas or deltas, and it is 

 further stated that Sphenophyllales are not essentially aquatic 

 plants. The Lycopodiales were, however, particularly adapted for 

 growth in mud or water, and Cordaitales also showed more vigour 

 m a like habitat. 



