FORMATION OF MOUNTAINS. 819 



oblique, a monoclinal uplift might be produced by shoving along it. 

 An incipient geanticlinal might be the first step toward such a fracture, 

 according with Daubree's illustrations (Fig. 1155) on page 801. The 

 volcanoes on the borders of the Pacific, and in other regions, stand 

 on lines of great fractures; but evidence that elevations of the 

 earth's crust were made along them at the time of disturbance cannot 

 often be made out. 



Further : the pressure either side of such a fracture might cause 

 elevation along it through the uplifting action of liquid or plastic ma- 

 terial thus forced up from below; a result that has often attended 

 ejections on a large scale. (Page 747.) 



3. Through the Slow Progress cf a Geosynclinal and of Sedi- 

 mentary Formations within it, ending in Fracture. 



From the facts which have been presented and partly recapitulated 

 on pages 785-807, and general facts and principles connected with the 

 physics of the globe, the following are the probable steps of progress 

 in this kind of mountain-making, of which the Appalachians are a 

 good example. 



1. Steps of Progress. — (1.) As a preparatory step, a geosynclinal 

 gradually deepens through a very long era, over a region of great ex- 

 tent, not much below the sea level ; and, concurrently, at equal rate, 

 or nearly, depositions of sediments take place in it, and thus make a 

 great pile of material for the future mountain structure. 



(2.) The making of such a geosynclinal, or downward flexure of 

 the crust, presupposes the making of a geanticlinal, or upward flexure 

 on one side or the other, or on both sides, since the two kinds of 

 flexures are complements of one another in the results of lateral 

 pressure. The former would displace, as it descended, some mobile 

 material of the earth's interior, which would go to fill the space made 

 beneath the latter. Facts appear to show that such a geanticlinal ex- 

 isted to the east, but not to the west ; and this accords with the fact, 

 elsewhere established, that the lateral pressure acted unequally from 

 the two opposite directions, the oceanic and continental, or had its 

 shoving side and its virtually resisting side. 



On the east side of the Appalachian trough the coast region was more elevated than 

 now, not only through the Carboniferous, but also through the following Triassic and 

 Jurassic periods, so that the coast-line was far outside of its present limit; for no beds 

 of these eras containing marine fossils occur along eastern Pennsylvania or to the north- 

 east. There is reason for concluding that the barrier existed also in the Trenton 

 period; for, while in the earlier Lower Silurian the life of the eastern border was, in 

 some points, like that of Europe, this was hardly at all so then. Gravity is against the 

 permanence of such upward flexures, and it may be for this reason, and because there 

 was a relief for the pressure in some other direction, that this geanticlinal disappeared. 

 In Cretaceous times the present sea-shore region was replete with life. 



