PALEOZOIC SEAS AND BARRIERS IN EASTERN NORTBt 



AMERICA! 



BY E. O. ULRICH A2sD CHARLES SCHUCHERT 



The following brief statement of the results of a series of 



"Ml 



important determinations in Appalachian geology anticipates a 

 fuller discussion of the abundant facts on which they are based 

 and which we hope to publish before the close of another year. 



For more than half a century the problems for which it is be- 

 lieved a rational solution is herewith tendered, have engaged the 

 attention of North American geologists. All who have worked 

 on any part of the Appalachian region have observed a great 

 difference in the stratigraphic succession as soon as they 

 entered the area lying just west of the Appalachian protaxis. 

 However careful their investigations, something has remained to 

 be explained, and many ingenious suggestions were offered, with- 

 out, save obscurely in one instance, attaining the true solution. 

 Stratigraphic continuity was assumed, and the more fragmental 

 character of the sediments along the western flank of the pro- 

 taxis was belicAxd to indicate little more than proximity to the 

 eastern shore line of the interior sea, while the interruption in 

 the gradual change eastward in the character of the deposits 

 was generally ascribed to overthrust faulting. 



But these explanations satisfied neither the stratigrapher nor 

 the paleontologist, and they were accepted only because no bet- 

 ter solution of the difficulties was at hand. The fact is, they 

 did not explain and w^ere mere makeshifts, necessitating one 

 assumption after another as detailed mapping progressed. 



Apparently the accepted solution did not satisfy that excellent 

 stratigrapher, Sir William Logan, who, in checking the results of 

 his investigations, enjoyed the advantage of close association 

 with so careful and able a paleontologist as E. Billings. With 

 a little more light Logan might have grasped the full signifi- 

 cance of the stratigraphic discordance prevailing so constantly 



^Published by permission of the director of the U. S. geological sui'vey 

 and of the secretary of the Smithsonian institution. 



