GEOLOGICAL SUCCESSION 293 



For the Piedmont of southeastern New York, Merrill* gives the fol- 

 lowing succession : 



Silurian : Hudson schist. 

 Cambro-Silurian : Stockbridge dolomite. 

 Cambrian : Poughquag quartzite. 

 Pre-Cambrian : Fordham gneiss. 



In the Maryland Piedmont, Mathews f has determined the following 

 series : 



Silurian: Peach-bottom slates, Cardiff quartz conglomerate. 



Wissahickon mica-schist, including an upper phyllite 

 member. 

 Cambro-Ordovician : Cockeysville marble. 

 Cambrian : Setters quartzite. 

 Pre-Cambrian : Baltimore gneiss. 



In the District of Columbia, in Virginia, North Carolina, and Ten- 

 nessee, Keith X includes the mica-schist, mica-gneiss, and granite-gneiss 

 under the division : 



Pre-Cambrian or Archean Carolina gneiss. 



The Pennsylvania Piedmont shows a similar series of arenaceous, cal- 

 careous, and argillaceous sediments. 



SEDIMENTARY SERIES OF THE SOUTHEASTERN BELT 



This belt contains the full series of sedimentary formations found to 

 the westward in the Pennsylvania Piedmont. The original character and 

 structures of these formations, however, have been rendered more obscure 

 than is the case with the western belt by greater metamorphism, due 

 both to dynamic forces and to the injection of great masses of acid and 

 basic igneous materials. 



The sedimentary series has been completely recrystallized and indu- 

 rated ; the argillaceous sediments have been converted into gneisses and 

 schists ; the arenaceous sediments into quartzite and quartz-schists ; the 

 calcareous material into marble. 



The dynamic forces which have metamorphosed the sediments were 

 generated by tangential thrust in southeast-northwest direction, which, 

 combined with gravity, has also produced longitudinal folds, striking 

 northeast, cleavage normal to the compressive force, and fissility both 

 normal and diagonal to the force. 



* New York City Folio, no. 83, U. S. Geol. Survey. 

 fThe American Journal of Science, vol. xvii, February, 1A04, p. 143. 

 X The Washington Folio, no. 70, U. S. Geol. Survey. 

 The Asheville Folio, no. 116, IT. S. Geol. Survey. 



