HYPOGEIC WORK. 387 



Virginia south west ward, along a series of Taconic geosynclines that ended 

 in the making of a series of Taconic ranges, on a line east of the Appala- 

 chian Range. See further, pages 531, 532. 



4. Geanticlines corresponding to the geosynclines. — It is not always easy 

 to identify the one or more geanticlines that the sinking of a geosyncline may 

 have produced. In the case of the Taconic and Appalachian ranges little 

 doubt exists. When the Taconic Range was completed, already a low geanti- 

 cline had risen above the continental sea, making two large islands between 

 southern Ohio and Alabama, one over the region of Cincinnati and part of 

 Kentucky, and the other in the same line over Tennessee. The region, 

 often called that of the Cincinnati uplift, was first identified as a Middle 

 Silurian emergence by J. S. Newberry and J. M. Safford. Moreover, an 

 eastern geanticline also showed itself; for the whole Atlantic border from 

 New York southwestward through Virginia and beyond became emerged at 

 the same time, and continued so, with probably increasing height through 

 the Upper Silurian, Devonian, and Carboniferous eras, when the making of 

 the Appalachian Range took place ; and also after this, through the Triassic 

 and Jurassic periods until the Middle Cretaceous ; for through all this time 

 no beds with marine fossils were formed over this great area. 



The contraction theory of mountain-making, as is seen, appeals to an all- 

 pervading force that must have been at work from the time the earth first 

 had a solid exterior. Already in later Archaean time it had made Archsean 

 mountain ranges ; and it is manifest, from succeeding events, that through- 

 out all time one system of evoliTtion was in progress. Moreover, the theory 

 has the virtue of explaining the facts, which is not true of the gravitation 

 theory. No other adequate explanation has been proposed. If the calcula- 

 tions of physicists do not give a sufficient depth for the results to the "level 

 of no strain," then the calculations may be believed to be in error until 

 some other adequate cause of the great faults and flexures has been brought 

 forward. 



5. Relations of mountain ranges to denudation. — Carving, gouging, and 

 leveling through denudation go on very rapidly in elevated regions of even a 

 moderate amount of rain, and have gone on through long ages since the rocks 

 were made, so that the original forms of the anticlines and synclines of 

 mountain ranges have disappeared, generally leaving ridges where synclines 

 once existed. 



Yet the geologist may still have little difficulty in tracing out the plica- 

 tions, even if the region over which they extend is now a level plain. The 

 investigator looks for evidence of folds in change of dip. If, on his way 

 westward over a region, he finds eastward dips changed to westward, he has 

 passed the axis of an anticline ; and if, going farther, he finds westward dips 

 changed to eastward, he sees proof that he has reached the axis of a syn- 

 cline. Complexities are added by the great faults, making difficulties which 

 can hardly be surmounted without the aid of fossils. 



From the facts presented in the above review of the structure of moun- 



