Barrell — Groivth of Knowledge of Earth Structure. 159 



simple mountains or mountain ranges that are the product of 

 one process of making — may have received, at the time of their 

 original making, no elevation beyond that resulting from 

 plication. 



This leads us to a grand distinction in orography, hitherto 

 neglected, which is fundamental and of the highest interest in 

 dynamical geology; a distinction between — 



1. A simple or individual mountain mass or range, which is 

 the result of one process of making, like an individual in any 

 process of evolution, and which may be distinguished as a mono- 

 genetic range, being one in genesis; and 



2. A composite or poly genetic range or chain, made up of 

 two or more monogenetic ranges combined. 



The Appalachian chain — the mountain region along the 

 Atlantic border of North America — is a poly genetic chain; it 

 consists, like the Rocky and other mountain chains, of several 

 monogenetic ranges, the more important of which are: 1. The 

 Highland range (including the Blue Ridge or parts of it, and 

 the Adironclacks also, if these belong to the same process of 

 making) pre-Silurian in formation; 2. The Green Mountain 

 range, in western New England and eastern New York, com- 

 pleted essentially after the Lower Silurian era or during its 

 closing period; 3. The Alleghany range, extending from south- 

 ern New York southwestward to Alabama, and completed 

 immediately after the Carboniferous age. 



The making of the Alleghany range was carried forward at 

 first through a long-continued subsidence — a geosynclinal (not 

 a true synclinal, since the rocks of the bending crust may have 

 had in them many true or simple synclinals as well as anti- 

 clinals), and a consequent accumulation of sediments, which 

 occupied the whole of Paleozoic time; and it was completed, 

 finally, in great breakings, faultings and foldings or plications 

 of the strata, along with other results of disturbance. 



11 These examples exhibit the characteristics of a large class 

 of mountain masses or ranges. A geosynclinal accompanied by 

 sedimentary depositions, and ending in a catastrophe of plica- 

 tions and solidification, are the essential steps, while metamor- 

 phism and igneous ejections are incidental results. The process 

 is one that produces final stability in the mass and its annexation 

 generally to the more stable part of the continent, though not 

 stable against future oscillations of level of wider range, nor 

 against denudation. 



It is apparent that in such a process of formation elevation 

 by direct uplift of the underlying crust has no necessary place. 

 The attending plications may make elevations on a vast scale 

 and so also may the shoves upward along the lines of fracture, 

 and crushing may sometimes add to the effect; but elevation 

 from an upward movement of the downward bent crust is only 

 an incidental concomitant, if it occur at all. 



