GENERAL OBSERVATIONS. 411 



"Whoever tries to work the problem will emerge from his calculation satisfied 

 that the force was vast. 



4. The force ivas slow in action and long continued. — That the move- 1 

 xnent must have been slow in progress, the flexures forming by a 

 movement of a few feet or yards in a century, continued through a 

 long time, is evident from the regularity of the stratification not- 

 withstanding the majestic system of foldings ; for there is no chaos: 

 the beds remain in their old order, only bent into arches and bold 

 flexures. The brittle rock experienced the force so gradually that 

 it yielded with little fracture, except along the axes of the folds, 

 where the strain was greatest. The folds were sometimes pressed 

 over until their tops projected westward over their bases, — which 

 could have been done only by a force acting with extreme slow- 

 ness. -There may have been sudden starts, and earthquakes be- 

 yond modern experience, but the general course of progress must 

 have been quiet. 



5. Heat. — Several thermal springs exist in Virginia, situated, ac- 

 cording to Rogers, along the axes of the Appalachian folds, as if 

 some traces of the heat in action still remained. 



4. Identity of the force with that causing movements in 

 earlier time. 



The force was the same in kind, and also in direction, judging 

 from the identity of results, with that which produced the flexures 

 and other changes that closed the Azoic age (p. 143); the same that 

 caused the oscillations through the progressing Palaeozoic ages re- 

 quired for the completion of the succession of rocks ; the same 

 that occasioned the deep subsidences along the Appalachian region. 



The Atlantic coast along New England varies much from its 

 general course. But this is only a repetition of an Azoic fact. The 

 line has a parallel in the Green Mountains with the westward bend 

 through New Jersey and Pennsylvania, and a still earlier parallel 

 in the outline of the New York Azoic. 



"When the Appalachian subsidences were about to cease, then 

 began the new movement that flexed and stiffened the rocks of 

 the Atlantic border. 



Although there is no proof in the flexures, or the metamorphism, 

 of any emergence of the strata from the ocean during their pro- 

 gress, there is sure evidence that when the revolution ceased it left 

 the Appalachian chain with at least its present elevation. The 

 evidence of this final result of the moving forces is afforded by the 

 strata of Mesozoic time, which come next under consideration. 



