102 



PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 20, 



On the other hand, I have not as yet been able to bridge over the 

 gulf which separates the flora of the Lower Carboniferous Coal- 

 measures from that of the Middle Coal-formation, an interval which 

 may include much of the " Lower Coal-measures" of Eogers in the 

 Pennsylvania Coal-field. 



Turning to that broader view which takes the prevalent conditions 

 of each portion of the period as characteristic, notwithstanding the 

 local existence of dissimilar conditions, we not only find, as already 

 stated, that the sequence in JS'ova Scotia coincides generally with 

 that in other parts of America and in Europe, but that, viewed in 

 this aspect, the Carboniferous period constitutes one of four great 

 physical cycles, which make up the Palaeozoic age in Eastern 

 America — and each of which was characterized by a great subsidence 

 and partial re-elevation, succeeded by a second and very gradual 

 subsidence. Viewed in this way, the Lower Carboniferous conglo- 

 merate and Lower Coal-measures correspond analogically with the 

 Oriskany Sandstone, the Oneida and Medina Sandstones, and the 

 Potsdam and Calciferous. The Carboniferous Limestone corresponds 

 with the Corniferous Limestone, the Niagara Limestone, and the 

 Trenton group of limestones. The Coal-measures correspond with 

 the Hamilton group, the Salina group, and the Utica Shale. The 

 Upper Coal-formation corresponds with the Chemung, the Lower 

 Helderberg, and the Hudson -River groups. The Permian is not 

 represented in Eastern America; but as developed in Europe it 

 clearly constitutes a similar cycle. These parallelisms, which deserve 

 more attention from geologists than they have yet received, may be 

 tabulated thus * : — 



Tabular View of Cycles in the Palaeozoic Age in Eastern America. 

 (The several formations are arranged in descending order.) 



Character of group. 



Lower 

 Silurian. 



Upper 

 Silurian. 



Devonian. 



Carbo- 

 niferous. 



Shallow, subsiding marine 

 area, filling up with sedi- 



VHudson-Eiver 

 ; group. 



^ Utica shale .. 



/Trenton, Black 

 -j E. and Chazy 

 \ limestones. 

 \ Potsdam and 

 y Calciferous 

 ) sandstones. 



Lower Helder- 

 berg group. 



Salina group. . 



Niagara and 



Clinton 



limestones. 

 Oneida and 



Medina 



sandstones. 



Chemung gr. . . 



Hamilton gr. .. 



Corniferous 

 limestone. 



Oriskany sand- 

 stone. 



Upper Coal- 

 formation. 



Coal-mea- 

 sures. 



Lower Carbo- 

 niferous lime- 

 stone. 



Lower Coal- 

 measures and 

 conglomerate. 



Elevation, followed by slow 

 subsidence, land-surfaces, 

 &e 



Marine conditions; forma- 

 tion of limestones, &c. . . 



Subsidence ; disturbances ; 

 deposition of coarse sedi- 

 ment 





In the Permian of Europe, the Stinkstein, the Eauchwacke, the 

 Zechstein, and the Eothhegendes might form a fifth parallel column. 



has more recently studied the Marine Limestones, has obtained facts which seem to 

 indicate the possibility of a more minute subdivision than any hitherto attempted 

 of these beds. 



* Dr. Sterry Hunt has directed attention to them in a paper " On Bitumens," 

 * Silliman's Journal ' [2], xxxy. p, 166, and in the ' Geology of Canada,' 1863, 

 p. 627 ; and Dana refers to them in his ' Manual of Geology.' Eaton and Hall 

 had previously noticed these parallelisms. 



