GENERAL OBSERVATIONS. 395 



V. DISTURBANCES CLOSING PALEOZOIC TIME. 

 1. American. 



An account of the Green Mountain revolution, closing the Lower 

 Silurian, has been given on pages 212-216. In the succeeding eras, 

 through the Paleozoic, — eras of prolonged quiet, — there were slow 

 oscillations in progress over the continent, and, at the close of the De- 

 vonian, some great displacements of strata, producing metamorphism, in 

 the northeast ; but no upturning took place over the Appalachian re- 

 gion southeast of New England, until the Carboniferous age was ap- 

 proaching, or had reached, its end. This epoch of disturbance even 

 rivalled that of the Middle Silurian, in the extent of the region in- 

 volved, and forms a historical boundary between Paleozoic and Meso- 

 zoic time. The upturning after the Lower Silurian affected the Green 

 Mountain region and some other parts of New England, folding and 

 crystallizing the rocks, besides raising the mountains above the sea and 

 adding them to the stable land of the Continent. In the disturbance 

 closing the Paleozoic, all of the Appalachian region southwest of the 

 Green Mountains was concerned ; and the Alleghany Mountains were 

 among the grand results. A portion of eastern New England, and of 

 New Brunswick and Nova Scotia to the northeast, partook in the 

 changes. It was a time of growth for the Continent; for, besides mak- 

 ing the Appalachians, nearly all the region east of the Mississippi be- 

 came part of the essentially stable land. 



The effects of the disturbance were like those of the Silurian revo- 

 lution. There were (1) flexures and upturnings of the strata; (2) 

 faults; and (3) alterations of rocks. 



1. Flexures. — The Coal-measures of Pennsylvania, Rhode Island, 

 and Nova Scotia, which were originally spread out in horizontal beds 

 of great extent, are now tilted at various angles, or rise into folds ; 

 and the strata are broken and faulted on a grand scale. Some of the 

 folds are scores of miles in breadth, and are in many successions 

 over the region, wave succeeding wave. Moreover, not only the Coal- 

 measures, but the Devonian and Silurian, with, in some regions at 

 least, part of the Archaean beds beneath, are involved together in this 

 majestic system of displacements. The following facts on this subject 

 are mainly from the Memoirs and Geological Reports of the Profes- 

 sors Rogers. 



The general character of the flexures is illustrated in the annexed 

 sections. Fig. 699 (by Taylor) is from the anthracite strata of the 

 Mauch Chunk region, Pennsylvania. The great coal bed is folded 

 and doubled on itself; and part of the inclosing strata are nearly ver- 

 tical. In Fig. 700 (by Rogers), from Trevorton, Pa., the folding is of 



