334 A. KEITH OUTLINES OF APPALACHIAN STRUCTURE 



time down to the present. The principal movements are given in the 

 following list : 



ArclieoM: Intrusion of batholiths; folding. 



Late Algonkian: Intrusion of batholiths: lava extrusions; eastward tilt- 

 ing in Appalachian region. 



Lower Camhiian: Deposition in Appalachian region. 



Upper Camhrian: Westward tilting; submergence of eastern United 

 States. 



Early Ordovician: Westward tilting; slight local folding in Xew Eng- 

 land, Tennessee, and Alabama. Uplift of Llanoria; Ouachita geo- 

 syncline deepened. 



Late Ordovician: Westward tilting of Appalachian region; slight local 

 folding in southeastern Xew A^ork, Xew Jersey, Maine, and Xew 

 Brunswick. 



Late Devonian: Intrusion of granite batholiths in Xew England and 

 Xew Brunswick; lava extrusions and folding in Maine and Xew 

 Brunswick. Slight folding and tilting in Illinois; uplift of south 

 part of Ozark dome. 



Mississippian (late) : Uplift of Ozark dome. Strong tilting, perhaps 

 folding, in Llanoria with volcanic activity. 



Late Pennsylvafiian : Strong folding in Arkansas and Oklahoma. 



Permian: Appalachian revolution; intrusion of granite batholiths. 



AMOUXT OF FOLDIXG 



The characters in which the Appalachian system differs most from the 

 rest of Xorth America are its linear aspect and the intensity with which 

 the rocks of the crust have been folded and piled up on themselves. The 

 amount of compression and shortening of the earth's crust thus made 

 evident is very great and has always been recognized as of great impor- 

 tance in the consideration of mountain-building. Many estimates have 

 been made of the total amount of this shortening in a northwest-south- 

 east direction. All of them have been seriously underestimated because 

 only the folded Paleozoic strata were considered; some of the estimates 

 have been insufficient even for these rocks, because they have been made 

 in regions where the shortening was least and was satisfied by open folds 

 with few or no faults. 



Estimates made by the author show a shortening of 30 to 60 per cent 

 of the original width of the folded belt. In all these estimates a geo- 

 metrical restoration was made, the folds being given the minimum possi- 

 ble height and the faults the least possible throw. For the Paleozoic 



