GEOLOGICAL CYCLES. 



137 



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

 stated, that the sequence in Nova Scotia coincides generally Avith 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 Paleozoic 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 conglomerate and 

 Lower Coal measures correspond analogically with the Oriskany sand- 

 stone, the Oneida and Medina sandstones, and the Potsdam and 

 Calciferous sandstones. The Carboniferous limestone corresponds with 

 the Corniferous limestone, the Niagara limestone, and the Trenton 

 group of limestones. The coal measures correspond with the Hamil- 

 ton 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 geolo- 

 gists than they have yet received, may be tabulated thus : — * 



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

 (The several formations are arranged in descending order.) 



Character of Group. 



Shallow, subsiding marine 1 

 area, filling up with sedi- >- 

 ment J 



Elevation, followed by slow ) 

 subsidence, land-surfaces, J- 

 etc j 



Marine conditions; fonna- ( 

 tion of limestones, etc ( 



Subsidence ; disturbances ; 

 deposition of coarse sedi- 

 ment 



Lower 

 Silurian. 



Upper 

 Silurian. 



Devonian. 



Hudson-River. Lower Helder- Chemung gr. 

 group. berg group. 



Utica shale. 



Salina group. Hamilton gr. 



Trenton, Black Niagara and 

 R. and Chazyi Clinton 

 limestones. I limestones. 



Potsdam and Oneida and 



Calciferous 

 sandstones. 



Medina 

 sandstones. 



Corniferous 

 limestone. 



Oriskany 

 sandstone. 



Carbo- 

 niferous. 



Upper coal 

 formation. 



Coal measures. 



Lower Carbo- 

 niferous 

 limestone. 



Lower Coal 

 measures and 

 conglomerate. 



In the Permian of Europe, the Stinkstein, the Rauchwacke, the 

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

 Of course such parallelism might be variously expressed, by reckoning 

 a smaller or larger number of groups. Independently of these diff'er- 

 ent modes of statement, however, I believe that the basis of such 

 comparisons exists in nature, and that it will prove possible to sub- 



* Dr Sterry Hunt lias directed attention to tliem in a pajier " On Bitumens," 

 Silliman's Journal [2], xxx.v. p. IOC), and in the "Geology of Canada," 18G3, p. G'27 ; 

 and Dana refers to them in his " Manual of Geology." Eaton and Hall had previously 

 noticed these parallelisms. 



