334 Pre- Carboniferous Floras of North-Eastern America. [May 5, 



of the Brian flora, and an investigation of its conditions of growth and 

 relations to the Carboniferous flora. 



The term "Erian" is applied to the formations included between the 

 top of the Upper Silurian and the base of the Carboniferous, on account of 

 the uncertainties which have attended the subdivision and limitation of the 

 Devonian of Europe, and also on account of the immense area occupied by 

 these beds on the south and west of Lake Erie, and their admirable deve- 

 lopment with regard to subdivisions and fossils. The name " Erie Divi- 

 sion" was also that originally applied to this typical series by the geologists 

 of the Survey of New York. 



A large part of the paper was occupied with the revision of the Erian 

 flora, including the description of twenty-three new species, and more 

 ample descriptions of others previously known only in fragments. Large 

 trunks of Prototazites, from the base of the Lower Devonian, were de- 

 scribed, and full details given of the form, structures, and fructification of 

 two species of Psilophyton. The new genus Ormoxylon was described. 

 The genus Cyclostiyma was noticed, as represented by two species in Ame- 

 rica, and its foliage and fruit described for the first time. The genera of 

 the Erian Ferns were examined and corrected, and several interesting trunks 

 and stipes belonging to Tree-ferns were described. The fruits of the genus 

 Cardiocarpam were illustrated with reference to their structure. The 

 occurrence of Lepidophloios, Calamodendron, and other forms in the Middle 

 Devonian was noticed for the first time. 



The third part of the memoir was occupied with comparisons and general 

 conclusions. At the close of the Upper- Silurian period there was a great 

 subsidence of the land in Eastern America, proved by the wide extent of 

 the marine beds of the Lower Helderberg (Ludlow) group. It was on the 

 small areas of Lower-Silurian and Laurentian land remaining after this 

 subsidence that the oldest land plants known in the region flourished. 

 Re-elevation occurred early in the Devonian period, and the known flora 

 receives considerable extension in the shallow-water beds of the Lower 

 Erian. The subsidence indicated by the great Corniferous limestone inter- 

 rupted these conditions on the west side of the Appalachians, but not on 

 their eastern side. At the close of this we find the rich Middle- Devonian 

 flora, which diminishes toward the close of the period ; and, after the phy- 

 sical disturbances which on the east side of the Appalachians terminated 

 the Erian age, it is followed by the meagre and quite dissimilar flora of the 

 Lower Carboniferous ; and this, after the subsidence indicated by the Car- 

 boniferous limestone, is followed by the Coal-formation flora. 



If we compare the Erian and Carboniferous floras, we find that the 

 leading genera of the latter are represented in the former, but, for the 

 most part, under distinct specific forms, that the Erian possesses some 

 genera of its own, and that many Carboniferous genera have not yet been 

 recognized in the Erian. There is also great local diversity in the Erian 

 flora, conveying the impression that the conditions affecting the growth of 



