FOLDS, SALIENTS, AND RECESSES 313 



foundland it is about 280 miles. Between these maxima at the north 

 and south the Cretaceous transgression reduces the visible width of the 

 belt to about 80 miles near the Hudson. Over the entire width of the 

 folded belt overturned folds and thrust faults prevail. In Xew Bruns- 

 wick and Xew England Carboniferous sediments are involved in the 

 eastern half of the folded belt. In Georgia and the Carolinas Carbon- 

 iferous granites occupy great areas at the east. In Virginia and Penn- 

 sylvania no rocks later than Middle Ordovician are now visible east of 

 the Blue Eidge. The distribution of the Carboniferous sediments and 

 granites is shown in plate 4. The great width of the intensely folded 

 belt is of enormous importance, as will be seen when the Appalachian 

 deformation is considered in later pages in a quantitative way. 



Desckiptiox 



FOLDfi 



: ■ 1 



The folds of the Appalachians are very long and straight. Many single 

 folds are more than 100 miles long, and even this figure is far exceeded 

 by some structures, such as the anticlines of the Blue Ridge in Virginia 

 and the Green Mountains of Vermont. The folds are rarely symmetrical, 

 but one side, usually the northwestern, has steeper dips than the other. 

 In many cases the beds are pushed past the vertical until they are upside 

 down, and both sides of the fold dip in the same direction. Out of these 

 unsymmetrical or overturned anticlines develop breaks in the sequence, 

 or thrust faults, which, as a rule, dip to the southeast, like the axial 

 planes. Little brecciation or crushing attends these faults, and the strata 

 both above and below the fault plane tend to have similar dips. Faults 

 of another class, called overthrusts, have no clear relation to individual 

 anticlines but cut across great thicknesses of strata. They are charac- 

 terized by great horizontal motion and by the low dip of their planes. 

 Locally, these faults have been folded and cut through by later faults. 



HALIEXT^ AXD RECESSES 



The folds are close together and for great distances run almost exactly 

 parallel. To the traveler through the country the strata upturned along 

 the folds seem to run perfectly straight for mile after mile, but in reality 

 they sweep in long parallel curves as if dra^vn with a radius around a 

 common center. In four districts, about 100 miles apart, the sweep of 

 the axes carries the folds around four great westward salients or projec- 

 tions from the average course of the system, which is from southwest to 

 northeast. These are (1) near the junction of Xorth Carolina and 



