the Earth's Contraction from Cooling. 213 



taring crinoids, corals, and mollusks, and making limestones. If 

 not westward, then it passed eastward-, and if driven eastward, a 

 geanticlinal elevation of a sea-border region parallel with the 

 area of subsidence must have been in progress from lateral pres- 

 sure. The height of this geanticlinal, or swell of the over- 

 lying crust (anticlinorium), would depend on the distance to 

 which escape eastward was possible — that is, on the eastward 

 extent of the subterranean region of mobile rock. Its elevation 

 was probably small and of varying extent during the Silurian 

 and Devonian ; for Devonian fossils show that the sea-border 

 south of New York had some way an open connexion with the 

 Atlantic Ocean; but there is no evidence in the Appalachian 

 rocks of the Carboniferous era to prove that off New Jersey it 

 was not at that time almost or quite a complete barrier : the 

 marine fossils in the more eastern of the Pennsylvania Coal- 

 measures are rare ; and those in the western Pennsylvania beds 

 would be from the waters of the Mediterranean Sea over the 

 Mississippi basin, which reached northward from Alabama and, 

 east of the Cincinnati uplift, bathed all the western part of the 

 Appalachian region, and probably its whole breadth. 



When, at the beginning of the making of the Alleghanies, 

 the strata commenced to yield before the pressure and to become 

 pushed up into great folds, the geanticlinal of the sea-border 

 would subside in part in consequence of the removal of re- 

 sistance in front of it; and this tendency to subside by gra- 

 vity may have been part of the means by which the plication 

 was made to go forward, its action adding to that of the pres- 

 sure. But the subsidence did not continue to the obliteration 

 of the geanticlinal ; for it was still above the ocean's level during 

 the following era — the Triassico-Jurassic. The absence of all 

 remains of distinctively marine fossils from these rocks, and from 

 any rocks of the Triassic and Jurassic eras in view over the Atlantic 

 border, demonstrate (as I have long held) that an emerged area 

 then existed outside of the present coast-line. Moreover, inas- 

 much as these Triassico-Jurassic areas (situated on the Atlantic 

 slope parallel with the Appalachians) were subsiding while their 

 rocks were in progress, the sea-border anticlinorium should at 

 the time have taken another turn upward as a counterpart to this 

 subsidence. 



With the close of the Triassico-Jurassic era, if not before, the 

 great anticlinorian barrier began actually to disappear ; and by 

 the time the Cretaceous period opened it had so far sunk that 

 the Atlantic coast-region south of New York was again exposed 

 to the ocean and flourished with abundant marine life, the Cre- 

 taceous fossils of the coast giving full evidence on this point. 

 Thus the absence from the present Atlantic border of all Triassic 



