328 INDEX TO THE STEATIGRAPHY OF NOETH AMERICA. 



too ambiguous to be at present of stratigraphic value. The correlative significance of Sporan- 

 gites jacksoni, which has not been found elsewhere, is also as yet undetermined. The remaining 

 species which comprise the main body of the Perry flora are Devonian. 



As will have been seen in the foregoing review, the evidence of the geologic distribution, so 

 far as known, of the identical species, of the genera themselves, and of the most nearly related 

 plant forms indicates distinctly and overwhelmingly a Devonian age for the Perry formation. 

 The stratigraphic range of most of the species and their alhes strongly points to a place in the 

 upper Devonian, the preponderance of the evidence being in favor of the Catskill-Chemung 

 stage. Allowing for the full weight of the two or three species of close lower Carboniferous 

 affinities, the flora can not at latest be assigned to a stage above the upper Catskill as developed 

 in northeastern Pennsylvania and southeastern New York. Compared with the flora of other 

 continents the closest paleontologic affinities of the Perry flora are found ia the plant associations 

 of the Donetz and of the Arctic Devonian. 



The occurrence of closely related species of Barinophyton and Leptophlseum together with 

 Archasopteris in the Devonian of Austraha affords an interesting example of the remarkable 

 intercontinental distribution of the later Devonian plant types. 



The conclusions as to the age of the Perry beds recorded long ago by Sir WilHam Dawson 

 are fully corroborated by the study of more extensive material and the discovery of additional 

 plants. 



The Devonian of Aroostook County, Maine, is discussed by Williams and 

 Gregory .®^^* Williams gives the following classification of the local subdivisions: 



Recent investigation of the rocks of the northern part of Aroostook County has brought 

 to fight a few facts regarding the stratigraphic terranes, which may be stated with some degree 

 of precision. 



There are a few well-marked groups of rocks which are distinguishable by their fithologic 

 characters, and the relative age of which is determined by their contained fossils. The order 

 which the present knowledge of the faunas seems to indicate is as follows: 



Devonian : 



9. Mapleton sandstone. 



8. Moose River sandstone. 

 Silurian : 



7. Chapman sandstone. ["] 



6. Square Lake limestone. ["] 



5. Ashland limestone. 



4. Ashland shales. 



3. Sheridan sandstone. 



2. Graptolite shales. 



1. Aroostook limestone. 



Below the Aroostook limestones are slates, which it is beheved are of Cambrian age, but 

 positive evidence of^he age is wanting. 



The lower seven belong to the Silurian; the upper two to the Devonian. The paleon- 

 tologic evidence is clear in placing 1 to 5 below the Lower Helderberg horizon of the New York 

 series. 



The Aroostook limestone, on both stratigraphic and paleontologic grounds, is befieved to 

 be older than any other of the terranes mentioned in this fist. 



The Ashland limestone, Ashland shales, and Sheridan sandstone are faunally closely asso- 

 ciated and belong together as the representatives of the Clinton-Niagara of the New York 

 standard. 



The Graptohte shales the writer befieves to be of Clinton age, but their stratigraphic posi- 

 tion in the Maine series is not satisfactorily estabfished. They may belong in the midst of the 



''Now known to be of Devonian age. — B. W. 



