174 C. SCHUCHERT THE XORTH AMEKICAX GEOSYNCLINES 



In other words, the sealevel attitude of the neutral area is not always in 

 keeping with the periodic sinkings of the geosyncline below sealevel. Ac- 

 cordingl}', there appears to be an irregular alternation between land and 

 sea conditions in the Appalachian, the ]\Iississippian, and the neutral 

 areas. 



Since the Appalachian trough is the type area on Avhich geosynclinal 

 structures are based, let us look a little more deeply into the local rock 

 quantities and times of sedimentation, so that we may learn more as to 

 the nature of its irregularly subsiding bottom. Accordingly, we will 

 present something of this detailed sedimentation along seven different 

 lines across the geosyncline. 



(1) Xorthivcst-soutlieast through Kingston. Xeic Yo)]c. — In this area the 

 maximum of sinking appears not to exceed 15.000 feet. Tlie generalized sec- 

 tion is about as follows : 



Feet 



Cambrian 1.500 



Ordovician 4,000 



Silurian (Shawangmik. 300: High Falls, 500; Cement series. 35) 835 



Devonian (Helderbergian, 250; Oriskany, 180; Esopus-Onondaga, 375; 



Hamilton. 1.300: Portage. 3,000; Chemmig, 1,725: eroded away. 500) . IMO 

 Mississippian eroded away .500 



14,165 



(2) Northwest-southeast through northern Neiv Jersey. — Here the maximum 

 of sinking appears to be about 23,000 feet. The generalized section is as fol- 

 lows : 



P>et 



Cambro-Ordovician (Chickies. 1.000 : Kittatinny, 3.000) 4.000 



Ordovician (.Jacksonburg. 150 ; Martinsburg. 3.000) 3,150 



Silurian ( Shawangunk. 1.600 ; High Falls. 2.300) 3,900 



Devonian ( Lower. 400 : rest. 8.500) 8.900 



Mississippian ( Susquehanna area ) 2,00(> 



Pennsylvanian (Anthracite area ) 1,500 



23,450 



(3) Through Mariiland and southern Pennsglvania. — This area appears to 

 be the second greatest subsidence (see 7). and the old Proterozoic land in the 

 deepest part of the trough has gone down about 35,000 feet. The detail is as 

 follows : 



Feet 

 Lower Cambrian (Autietam. 800; Harpers, 2,750; Weverton. 1.250: 



Tomstown, l,OfK) : Waynesboro, 1,250 ; Elbrook, 3,000) 10.050 



Cambro-Ordovician ( Conococheague, 1.635; Beekmautown, 2,.30O) 3.935 



Ordovician (Stones River, 1.050; Chambersburg. 750: Martinsburg, 



2,000 ; Juniata. 400) 4.200 



