W. Carruthers — Tree-ferns of the Coal-measures. 465 



great final depression one of oscillation. I have inferred the latter 

 as the actual condition during all this period of the sedimentary 

 accumulations. I am inclined to believe, moreover, that the alter- 

 nation of coarser and finer beds may be due to such action, and that 

 the pushing out of these coarser beds towards the v^estward, charged 

 as they are by a littoral fauna, may be due to the elevation of the 

 shore-line, and the consequent extension of such sediments. When 

 again the shore-line recedes, from the gradual submergence and de- 

 pression of this area below the sea-level, the finer sediments encroach 

 upon the area before occupied by the coarser ; the Brachiopoda suc- 

 ceed to the LamellihrancMata, and we have the alternation of coarser 

 and finer deposits, and the alternation of generations of essentially 

 the same species, with now and then the coming in of new forms. 

 Whether this view be tenable or not must depend on future con- 

 tinued and careful investigations. I had entertained this view from 

 the alternation in the character of the sediments and the fossils. The 

 discovery of this evidence of a shore-line, which afterwards became 

 submerged, and again elevated, and extended westward at a later 

 period, seems to offer some confirmation of the view. 



II. — On the Tree-ferns of the Coal-measures, and their 

 Affinities with Existing Forms. 



By "W. Caeruthers, F.E.S. 



LINDLEY and Hutton describe two species of Tree-ferns from 

 the Coal-measures, both from the Bath Coal-field. I have 

 been able to add eight species hitherto undescribed, chiefly through 

 the assistance of J. M'Murtrie, Esq., of Eadstock. These belong to 

 three groups, which are remarkably distinguished by peculiarities in 

 the structure of the stems. Two of the groups belong to living 

 forms, while the third is extinct, being confined to Palaeozoic forma- 

 tions. Caulopteris and TuhicauUs belong to the same type as the 

 living Ferns which possess stems, including under this term the 

 humijle stems (falsely called rhizomes) of many of our British 

 species, as well as the arborescent Ferns of warmer regions; and 

 excluding the rhizomatous forms like Fteris, Pohjpodium, and 

 Hymenophyllum. In all these stems we have a central medulla, 

 surrounded by a continuous vascular cylinder penetrated regularly by 

 meshes, from the margins of which the vascular bundle or bundles 

 to the fronds are given off, and through which the parenchyma of 

 the medulla is continuous with that of the stipes. In most Tree- 

 ferns the medullary axis is larger, and the bases of the stipes decay 

 down to the circumference of the stem; but in Osmunda the persistent 

 bases of the stipes permanently clothe the small vascular cylinder 

 which incloses a slender pith. To this latter form belongs the stipe 

 with a dumb-bell-shaped vascular bundle, separate specimens of 

 which I have obtained from the Coal-measures. These have been 

 described, both on the Continent and in this country, under the name 

 of Zygopteris, but they belong to Cotta's genus Tuhicaidis ; and they 



VOL. IX. — NO. c. . 30 



