LAND AND SEA OSCILLATIONS — TJLRICH. 



331 



the others- through the belt lying between Rome, Georgia, and Gads- 

 den, Alabama. 



These transverse axes do not cross the longitudinal troughs of the 

 geosyncline in continuous direct lines. On the contrary, their course 

 zigzags within the varying limits of a broad band, so that the north- 

 ern head of a bay in one trough may extend 50 miles or more beyond 

 the latitude of the southern head of another younger or older bay 

 in an adjacent trough. The band is wide enough and was always low 

 enough so that regional tilting occasionally perm 

 edges of formations transgressing from opposite d 



tted overlap of 

 rections. Often 



PIG. 2. — Diagram illustrating tilting of interior areas of uplift (for example, the Cincin- 

 nati dome), and the consequent variations in amounts of advance and retreat of the sea 

 on their opposite sides. Arrows indicate direction of horizontal stresses. The letters 

 A, A', A", on the one side, and B, B', and B", on the other, mark the same points 

 on the flanks of the dome in all of the three stages. In 1 the sea laps equally on both 

 sides ; in 2 the elevation of the dome is accentuated and its summit has migrated to the 

 left, while the sea has advanced much more on the right side than on the left ; in 3 the 

 summit has migrated in the opposite direction so that the deposits of the preceding 

 stage on the right flanks are largely emerged,, whereas on the submerged left flank the 

 new sea widely overlaps the deposits of the two preceding stages (1' and 2'). 



the axis formed an efficient barrier in one trough and was much less 

 effective in the one next to the west or east. More rarely, a bay, ter- 

 minated at the north by a transverse axis, connected laterally with 

 waters in an adjoining trough in which the submergence was not 

 stopped by the axis. Finally, at other times the axis offered no serious 

 obstacle to the passage of the marine invasion. Of course, the indi- 

 vidual troughs were submerged over and over again, but in none do 

 we find representatives of all of the formations known to have been 

 deposited in the Appalachian Valley. 



Varying geographic expressions like these could have been made 

 possible only by differential vertical movements in the concerned 



