442 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



The oscillations referred to in the first proposition did not disturb 

 the conformableness of the strata, because they operated on the whole 

 equally and simultaneously. 



II. The second proposition, namely, that the only great plutonic 

 disturbance in the palaeozoic series we are now concerned with took 

 place after the deposition of the coal-measures, rests on the following 

 considerations, among some others which will appear in the sequel : — 



1st. Because the disturbed country (the Appalachian Ridge) on 

 the Atlantic side of North America is gathered up and compacted 

 into one mass, and exhibits the working of a single cause, most power- 

 fully in the centre, less and less laterally, but nevertheless extending 

 sideways, in deep-seated throes, to great distances, and there showing 

 itself in broad undulations or low-arched domes, or in minor frac- 

 tures. 



2ndly. Because the axes or lines of uplift, both principal and sub- 

 ordinate, are continuous in nearly the same direction for the great 

 distance of 1500 miles, with the usual great transverse fissures, ac- 

 cording to the State-geologists employed in these regions. These 

 axes are sometimes in straight lines for 100 miles together, and in 

 one instance for more than 200 miles. 



3rdly. Because, in like manner, the dips and foldings, so close, 

 highly inclined, and sharp along the central line of disturbance, gra- 

 dually open wider and wider, become undulatory, and finally hori- 

 zontal continuously from stratum to stratum, as they depart west- 

 wards, and floor the flat countries there. 



4thly. Because the whole series of the palaeozoic formations of 

 Middle North-east America, from the oldest to the newest, was equally 

 affected over the tract of country just referred to ; the coal-measures 

 (the newest) fully partaking of the great and general disturbance, 

 becoming anthracitic, and then slowly returning to the bituminous 

 state, and to horizontality, as they pass into the Western plains, away 

 from the seat of elevatory action. This is universally admitted, and 

 has been beautifully explained by Professors W. B. and H. D. 

 Rogers. 



5thly. Because, as would occur in singleness of action, in most of 

 the other strata, the return westward to their original position and 

 mineral state is gradual — as is seen in the natural sections of the 

 Mohawk Valley, and about the head of Lake Champlain. The 

 proximity of the Atlantic Ocean, together with certain overlying 

 Tertiaries, prevents our observing this on the east of the Appalachian 

 Ridge. 



6thly. Because, as J. D. Dana (Address, Sill. Journ. n. s. xxii. 

 p. 311) expresses himself, "simplicity of structure is the feature of 

 American geology." Hence the lessened probability of oft-repeated re- 

 volutions ; which revolutions on the western continent are remarkable 

 for completeness, and for their clear exhibition of geological principles. 

 All this is in strong contrast with the complex and mangled condi- 

 tion of European palaeozoic formations. 



7thly. Because the upheavals, fractures, and inversions hinted at, 



