RISE or THE THEORY OF GEOSYXCLIXES 157 



cumulating sediments, an explanation which, he states, is "wholly at 

 variance with physical law." It was at this time that Dana introduced 

 the term geosyndines for what Hall had called synclines, because they 

 do not have the simple synclinal structure, but are made up rather of 

 "many true or simple synclinals as well as anticlinals.'^ The mountain 

 system that eventually rises out of a geosyncline, Dana at the same time 

 called a synclinoriiun. In other words, synclinorial mountains arise sub- 

 sequently, through folding due to lateral compression, out of the strata 

 of a geosyncline. 



"The term thus iiitroducecl by Dana has, unfortunately, been diverted from 

 its original meaning and applied to a general syncline compounded of minor 

 folds and contrasted with anticlinorium. It has thus become a term of struc- 

 ture, and the related idea of mountain-making, which the name expresses, has 

 been relegated to a subordinate position, or entirelj^ left out." " 



"The geosynelinal ranges or synclinoria have experienced in almost all cases, 

 since their completion, true elevation through great geanticlinal movements, 

 but movements that embraced a wider range of crust than that concerned in 

 the preceding geosynelinal movements — indeed, a range of crust that comes 

 strictly under the designation of a polygenetic mass." In other words, "Moun- 

 tain chains are combinations of synclinoria and of anticlinorian elevations." ^^ 



Dana in 1895 says further :^^ 



"The great facts to be explained in a theory of mountain-making relate (1> 

 to the preparatory geosyncline or trough and its load of strata for the moun- 

 tain structure; (2) to the mountain-making events — the upturning, flexing, 

 and faulting of the strata, and all other effects of the movements in progress. 

 On any theory of origin, such mountain ranges are synclinoria, as they have 

 been termed by the author, from the Greek for siincUne, and 6pos, mountain, 

 thej^ having had their beginning, as first recognized by Hall, in a preparatory 

 geosyncline of accumulation. The geosyncline occupied the area of the future 

 mountain range." 



T^VO KINDS OF GE0SYXCLIXE8 IX XORTH AMERICA 



Just as there are several categories of geanticlines, so there are at least 

 two types of geosyndines, some ( 1 ) with comparatively short and simple 

 histories, like the Acadian and Saint Lawrence troughs, or with longer 

 histories, like the Franklinian; and (2) others, very extensive in time 

 and space, having undergone long and complicated evolutions, as did the 

 Appalachian and Cordilleran (see maps, figures 1 and 3). 



In America, where the theory of geosyndines arose, the idea is tj'pified 

 by the structure of the Appalachian-Allegheny area, and it is admitted 



1" L. v. Pirsson : Text-Tjook of geology, Pt. I, Physical geology, 2d ed., 1920, p. 306. 



11 Dana : Op. cit., pp. 432, 171. 



1- Dana : Manual of geology, -Ith ed., p. 380. 



