176 C. SCHUCHERT THE NORTH AMERICAN GEOSYNCLINES 



least two major rock basins.^^ In eastern central New York (Albany) 

 the depression is probably somewhere near 8,000 feet. From here south- 

 ward the trough becomes ever deeper, and in western Maryland it ap- 

 pears to have gone doTvn abont 35,000 feet. Thence the bottom^rises 

 again to the Virginia-Tennessee State line to abont 20,000 feet, only to 

 sink rapidly in the Knoxville area to abont 30,000 feet and to about 

 38,000 feet in northeastern Alabama. What has gone on to the south- 

 ward is not ascertainable because of the Mesozoic overlaps from the Gulf 

 of Mexico. 



Just as the trough bottom evolved in long undulations along its strike,, 

 so in transverse directions it became more or less waved. This is best 

 seen in the narrow but long continuance of the very thick Lower Cam- 

 brian deposits in the southern part of the Appalachian geosyncline. Here 

 these strata in the eastern part of the trough attain a thickness of about 

 15,000 feet, and thin rapidly to the west. The trough in early Ordo- 

 vician time was a far wider subsiding syncline, and in the middle part 

 of this period the extreme eastern portion appears for a time to have 

 been divided into several long and narrow seaways. ^^ In the Maryland 

 region the Appalachian sea during Lower Cambrian time was also a nar- 

 row one, and here accumulated about 10,000 feet of strata. Then came 

 wider seas transversely, and the}' accumulated in their deepest part an- 

 other 10,000 feet during Ordovician and Silurian time. Over all came- 

 the great Devonian-Mississippian delta, so ably pictured by Willis and 

 Barrell,^^ depositing another two miles' depth of strata. Finally, in the 

 comparatively narrow Cahaba coal field of Alabama was deposited, ac- 

 cording to Butts,^^ 10,000 feet of early Pennsylvanian sediments. 



In all of this we see that the Appalachian geosyncline during its growth 

 evolved along its strike into at least two great basins of deposits, while 

 transversely the trough was variably wrinkled, changing more and more 

 from a simple syncline into a complex geosyncline. These greater undu- 

 lations of the bottom of the trough and of the older Paleozoic formations 

 should not be confounded with the later superimposed foldings due to- 



-^ Ulrich in his "Revision of the Paleozoic systems," this Bulletin, vol. 22, 1911, p. 

 562, divides the Appalachian geosyncline into five basins, as follows : (1) northeastern 

 Pennsylvania, (2) Maryland, (3) central Virginia, (4) Tennessee, and (5) Alabama. 



29 See Ulrich : Op. cit., p. 412. 



3" Bailey Willis : Paleozoic Appalachia, or the history of Maryland during Paleozoic 

 time. Maryland Geol. Survey, vol. 4, 1902, pp. 23-93. 

 Joseph Barren : Op. cit. 



31 Charles Butts : The southern part of the Cahaba coal field, Alabama. U. S. Geol. 

 Survey, Bull. 431, 1911, pp. 89-146. 



Charles Butts and E. O. Ulrich : Mississippian formations of western Kentucky. 

 Kentucky Geol. Survey, 1917, p. 118. 



