GEANTICLINES 167 



rence and the Acadian geosynclines on either side of it came into exist- 

 ence, namely, toward or at the close of the Proterozoic. This axis, begin- 

 ning in the granitic area of eastern Connecticut and Ehode Island, 

 continues across central Massachusetts into New Hampshire (the White 

 Mountains are situated on it), thence northeasterly across central Maine 

 into northern ISTew Brunswick, and finally across southern N^ewfounclland. 

 The width of this geanticline appears to have been on the average greater 

 than 100 miles. 



How often the New Brunswick geanticline was in upward motion is 

 not yet known. If, however, we may judge by the nature of the coarse 

 sediments in the Saint Lawrence trough, it appears to have been rejuve- 

 nated into a highland (1) toward the close of the Cambrian (seen in the 

 Lauzon quartzites and conglomerates, the red Sillery, and the green Que- 

 bec slates) ; (2) during the later Orclovician (seen in the coarse Cincin- 

 natian and early Silurian formations) ; and (3) by the long-continued 

 intermittent rising during late Silurian and middle Devonian time, 

 which ended in the Gaspe sandstones, 7,000 feet thick. 



The Ancestral Eocky Mountains geanticline and the Cordilleran Inter- 

 montane geanticline are best described in connection with the Cordilleran 

 geos3aicline (see pages 186-187). 



KINDS OF OEAXTICLINES 



The several geanticlines or anticlinoria of North America can bo 

 grouped in three categories: Those of lesser import are (1) the low, 

 narrow, localized arches in the interior of the continent, typified by the 

 Cincinnati arch. The most mobile of the anticlinoria are (2) the peri- 

 odically rising borderlands, such as Appalachia, which border the geosyn- 

 clines oceanward. They have been described on preceding pages and need 

 no discussion here. Then there are (3) the geanticlines that rise out of 

 the area of a geosyncline and have seas on either side of them, as the 

 New Brunswick, Ancestral Eocky Mountains, and Cordilleran Intermon- 

 tane geanticlines. 



Geanticlines may have no direct connection at all with folded moun- 

 tains, as in the Cincinnati arch. In other cases a geanticline is situated 

 on one side of an erogenic mass, aS the Front Eanges of Colorado lie in 

 front of the Eocky Mountains. In yet other cases folded mountains are 

 present on either side of a geanticline, as the Sierra Nevadas and the 

 Eocky Mountains on either side of the Cordilleran Intermontane geanti- 

 cline. The latter appears to be the equivalent of the "Narben" and the 

 "Zwischengebirge'' of Kober's Alpine orogen.-*^ Geanticlines and orogens 



20 L. Kober : Der Bau der Erde, 1921, p. 140. 

 XII — BrLL. Geol. Soc. Am., Vol. 34, 1922 



