DEVELOPMENT OF THE APPALACHIAN GEOSYXCLIKES 175 



Feet 



Silurian (Tuscarora, 270 ; Clinton, 920 ; Cayugan, 1,450) 2,640 



Devonian (Helderbergian, 300; Oriskany, 400; Romney, 1,400; Jennings, 



4,800 ; Hampshire, 4,700) 11,600 



Mississippian (Pocono, 1,800 ; Mauch Chunk, 2,000) 3,800 



Pennsylvanian, 3,100 ; Permian only in west, 1,200 4,300 



40,525 



(4) Through central Virginia and West Yirginia. — It appears that in this 

 area the trough did not subside more than 25,000 feet. The formations are as 

 follows : 



Feet 



Cambrian, probably 8,000 



Ordovician (Shenandoah, 2,400; Martinsburg, 2,000; Massanutten- 



Juniata, 1,000) 5.400 



Silurian (Tuscarora, 600 ; Rockwood, 700; Cayugan, 700) 2.000 



Devonian (Helderbergian, 200; Oriskany, 300; Middle, 1,300; Upper, 



5,000) 6,800 



Mississippian (Pocono, 500 ; Greenbrier, 1,0(X) ; Canaan, 1.200) 2,700 



Pennsylvanian, probably 4,000 



28,9D0 



(5) Through northeastern Tennessee and southwestern Virginia. — The sub- 

 sidence here appears not to have exceeded 20,000 feet. The thicknesses are 

 about as follows : 



Feet 

 Cambrian, 9,000; Ordovician, 6,000; Silurian, 1,000; Devonian. 300; 



Mississippian, 3,600 ; I'ennsylvanian, 5,000 24,900 



(6) Northivest and southeast through Knoxville, Tennessee. — The subsi- 

 dence here is at least 30,000 feet. The thicknesses are about as follows : 



Feet 

 Cambrian, 18,000; Ordovician, 8,000; Silurian, 1,200; Devonian, 50: 



Mississippian, 2,100 ; Pennsylvanian, 2,000 31,350 



(7) Northwest and southeast through northern Alahama. — Here the subsi- 

 dence is greatest, being around 38,000 feet. The detail is as follows : 



Feet 

 Cambrian (Weisner, 10,000; Beaver, 1,000; Rome, 800; Conasauga. 



3,000) 14,800 



Ordovician (Knox, 4,500 ; rest, 3,500) 8,000 



Silurian, 1,200 ; Devonian, 1,000 ; Mississippian, 3,250 5,450 



Pennsylvanian (Warrior field, 3,500; Caliaba, 5,500; Coosa, 10,000) 10.000 



38,250 



An analysis of the seven sections just given sliows that the bottom of 

 the Appalachian geosyncline has subsided in the line of its strike into at 



