CHAP. V.] DEVONIAN PERIOD. 67 



Lepidodendra, Cyclostigmce, and the splendid ferns known 

 as Palceopteris hibemica, the fronds of which are nearly two 

 feet in breadth. Eventually here and elsewhere the con- 

 tinued depression of the land brought the level of the lake 

 waters down to that of the Carboniferous sea, which was 

 gradually extending itself over the lower parts of the great 

 Devonian continent. 



This view of the relations of the so-called Upper Old 

 Red to the Carboniferous system has been well expressed 

 by Mr. B. N. Peach. 1 " As the land in the northern areas 

 gradually sank, the lacustrine and littoral deposits were 

 succeeded conformably by estuarine and marine strata of 

 Lower Carboniferous age, and a much newer facies of fish 

 fauna followed the Old Eed types. . . . This remarkable 

 palaeontological break in a conformable series of strata can 

 be satisfactorily explained if we regard the Upper Old Eed 

 fishes as the survivors of an older fauna still confined to 

 land-locked basins, while the Carboniferous forms suddenly 

 gained access to the Scottish area from the open sea, where 

 they had developed at a much more rapid rate than their 

 less favoured relatives." 



Whether the Welsh gulf continued open throughout the 

 whole period we are not at present in a position to say ; 

 possibly it was at times completely silted up and converted 

 into a low-lying tract of land, but it was under water again 

 during the formation of the Upper Old Red Sandstone, and 

 its limits were then greatly extended in an east and west 

 direction. The sea then probably stretched westward for 

 some distance toward Ireland, and was only separated by 

 narrow barriers from the lacustrine waters of that area. 

 When at length these barriers were submerged, and the 

 sea spread over all the lower parts of the great Devonian 

 continent, it ushered in a new fauna, and with this we com- 



1 "Proc. Roy. Phys. Soc. of Edinburgh," vol. ix. p. 13. 



