70 ME. D. DAVIES OS THE ECOLOGX OF [vol. Ixxvii, 



pebbles occur in the series at this juncture, accompanied by a great 

 increase of new species, we could fairly conclude that both geo- 

 logical and palseontological breaks occurred. 



YI. CoxcLrDiya Remaeks. 



The difficulty of arriving at a reasonable conclusion as to past 

 physical conditions will always remain. "We notice from the 

 evidence set forth that, throughout the ten horizons, there is a 

 good representation of marsh or swamp flora in the Equisetales, 

 also an even more persistent representation of a dry -laud tlora 

 in the Cordaitales throughout these horizons. On the other hand, 

 there is a dry-land flora, as represented by the ferns and fernlike 

 plants notably weak ; whereas the Lycopods (a swamp flora) are 

 abundant at the time when the ferns and fernlike plants were 

 extremely rare. Possibly the Equisetales always managed to 

 survive, even when great areas of elevated land-surface prevailed, 

 clothing perhaps the margins of the drainage systems, such as the 

 rivers, deltas, and the slopes near the open seas. Again, the Cor- 

 daitales possibly were very adaptable to altered physical conditions. 

 It would be well to state here that, whatever may be the reason, 

 the association of Cordaite-leaves and Calamites was of common 

 occurrence throughout in the same blocks of shale. On the other 

 hand, the Lycopods were not persistent (as already stated), and 

 only appeared in force at two horizons. A significant fact is 

 that the ferns and fernlike plants were nearly eliminated at this 

 junctui'e. A fm'ther point worthy of consideration is the fact 

 that prior to and after this period favouring the Lycopods, a 

 goodly number of ferns and fernlike plants appeared, whereas the 

 Lycopods were notably rare. Another point worthy of notice is 

 the fact that, when Lycopods were commonly found, their cones 

 were frequently associated in the same slabs of shale. It is quite 

 natural that, as the stems and shoots of the Lycopods were ti-ans- 

 ported from the point where they grew to the point where they 

 now rest in the sediments, the cones should also accompany them. 



It is reasonable to believe that, when possibly a 2>i'eponderance 

 of dry-land flora existed in the past, theu' balance, when ex- 

 amined in the shales, from a point of distribution, would greatly 

 alter, owing to the favoui'ed position of plants which grew near 

 running water, favoured in regard to future preservation of their 

 remains. 



Possibly we may conclude that the key to the problem of past 

 physical conditions is found in the ferns and fernlike plants 

 and the Lycopods. They doubtless reacted one on the other, 

 coincidently with the physical changes. If we believe that, 

 generally speaking, the ferns and fernlike plants were on the 

 whole a dry-land flora, and that the Lycopods represented a 

 swamp flora, then we are driven to the conclusion that upland 

 conditions prevailed from Five-Foot Seam times to Six-Foot 

 Seam times, followed bv a cvele of submergence of the elevated 



