750 DYNAMICAL GEOLOGY. 



in height, — a denudation, after pursuing its work for a while, would 

 reduce it to a group of synclinal ridges. The fractured anticlinals 

 are easily worn away; while the synclinals have the elements of 

 greater permanence, in being much less broken above, and in having 

 their rocks folded and pressed together, if a close synclinal, and thus 

 made firmer and more durable, even if not also crystallized by meta- 

 morphism. The synclinals of greatest breadth and depth, other things 

 being equal, will become ultimately the highest of the mountain 

 ridges, because more material is embraced in them. In the Taconic 

 Mountains, on the western border of Massachusetts, Mount Washing- 

 ton (including Mount Everett) and Graylock are the high peaks, for 

 the reason just explained. Other portions of the Taconic range are 

 made of narrower portions of the synclinal, and are less elevated. 

 (p.^213.) 



7. A Moicntain Chain may comprise Synclinoria of different ages. 

 — The Appalachian chain consists of (1) mountains of Archaean rocks, 

 that were made in pre-Silurian time ; (2) the Green Mountains, that 

 date from the close of the Lower Silurian ; and (3) the Alleghanies, 

 that were formed at the close of the Carboniferous age. The Green 

 Mountains began in the same great geosynclinal with the Alleghanies ; 

 but that northern part of it reached its completion and catastrophe 

 long before the Alleghany part, probably because so near the Adi- 

 rondack border of the stable part of the continent. It is probable 

 that the Archaean portion of the Appalachian chain, which includes 

 the Blue Ridge, the New Jersey Highlands, continued in Dutchess 

 County, N. Y., and the Adirondacks, corresponds to another older 

 synclinorium. Thus a mountain chain may comprise several syn- 

 clinoria made at widely different epochs. 



The several areas of the Triassico-Jurassic sandstone (p. 403) were 

 areas of subsidence or sinking troughs, and of sedimentary accumu- 

 lations in progress in each trough ; and the geosynclinal, in each case, 

 ended in catastrophe, as exhibited in upturned or displaced rocks, and 

 in many lines of great fractures, giving exit to igneous rocks. The 

 progress was like that in the case of a synclinorium, although no 

 true mountain-chain was made. 



8. Metamorphism and other attendant Effects. — The heat, developed 

 through the transformation of the motion, in the making of a range 

 by great flexures and fractures, would produce all the consolidation 

 and crystallization of the beds which has been, in any case, observed ; 

 and would cause, as lighter effects, the change of brown oxyds of iron 

 to red oxyd, thereby reddening sandstones and clays ; or make other 

 decompositions in which red oxyd of iron is developed ; and, as a 

 lighter effect, debituminize mineral coal, and evolve mineral oil from 



