108 THE GEOLOGICAL HISTORY OF PLANTS. 



undisturbed and unaltered rocks of this age, including a thickness 

 in some places of eighteen thousand feet, and extending from east 

 to west through the Northern States of the Union and western 

 Canada for nearly seven hundred miles, while it spreads from north 

 to south from the northern part of Michigan far into the Middle 

 States, is undoubtedly the most important Devonian area now known 

 to geologists. 2. This area has been taken by all American geolo- 

 gists as their typical Devonian region. It is rich in fossils, and 

 these have been thoroughly studied and admirably illustrated by 

 the New York and Canadian Surveys. 3. The rocks of this area 

 surround the basin of Lake Erie, and were named, in the original 

 reports of the New York Survey, the " Erie Division" 4. Great 

 difficulties have been experienced in the classification of the Euro- 

 pean Devonian, and the uncertainties thus arising have tended to 

 throw doubt on the results obtained in America in circumstances in 

 which such difficulties do not occur. 



These reasons are, I think, sufficient to warrant me in holding 

 the great Erie Division of the New York geologists as the typical 

 representative of the rocks deposited between the close of the Upper 

 Silurian and the beginning of the Carboniferous period, and to use 

 the term Erian as the designation of this great series of deposits as 

 developed in America, in so far at least as their flora is concerned. 

 In doing so, I do not wish to introduce a new name merely for the 

 sake of novelty ; but I hope to keep before the minds of geologists 

 the caution that they should not measure the Erian formations of 

 America, or the fossils which they contain, by the comparatively 

 depauperated representatives of this portion of the geological scale 

 in the Devonian of western Europe. 



VII. ON THE RELATIONS OF THE SO-CALLED " URSA STAGE " OF 

 BEAR ISLAND WITH THE PALAEOZOIC FLORA OF NORTH 

 AMERICA. 



The following note is a verbatim copy of that published by me 

 in 1873, and the accuracy of which has now been vindicated by the 

 recent observations of Nathorst : 



The plants catalogued by Dr. Heer, and characterising what he 

 calls the " Ursa Stage," are in part representatives of those of the 

 American flora which I have described as the " Lower Carboniferous 

 Coal-Measures " (Subcarboniferous of Dana), and whose characteristic 

 species, as developed in Nova Scotia, I noticed in the " Journal of 

 the Geological Society " in 1858 (vol. xv.). Dr. Heer's list, however, 

 includes some Upper Devonian forms; and I would suggest that 



