80 PROCEEDINGS OF THE NATIONAL MUSEUM vol.76 



rocks of these ages were deposited in North America constitute the 

 physical part of the evidence on which I base my claim that this is 

 one of the most important breaks in the Paleozoic column. And 

 the organic part of the evidence is no less impressive. The strati- 

 graphic significance of the gap between the two systems is narrowed 

 to its observed minimum in Lawrence Count}'^, Ark., where it is 

 reduced (1) by the insertion of tAvo formations at the top of the Cana- 

 dian that are not present elsewhere in the Ozark region and (2) by 

 the downward expansion of the Buffalo River series which attains its 

 maximum development in Newton County about 100 miles west of 

 Lawrence County. To the north and west of Newton County the 

 chronologic significance of the gap then increases rapidly to places at 

 which the Powell or even the Cotter — respectively, the third and 

 fourth formations beneath the top of the Upper Canadian — is direct- 

 ly succeeded by deposits of Mississippian age. Surely, conclusions 

 based on such data deserve respect and more general acceptance. 



Proceeding with the explanatory notes on the middle and southern 

 Appalachian column, the conventions employed indicate that the 

 Murfreesboro, Pierce, and Lebanon formations lap out eastwardly 

 and the Mosheim pinches out in the opposite direction. The Lenoir, 

 however, seems to extend completely across the valley in southwestern 

 Virginia and is supposed to have attained weak connection with 

 the Ridley in central Tennessee and Kentucky. But no such alter- 

 nation of Atlantic and southern invasions of the Appalachian geo- 

 syncline is indicated by the formations of the Blount group, all 

 of which are confined to the eastern half or two-thirds of the valley ; 

 and the succeeding Little Oak is found only in one or two of the 

 earstern troughs in Alabama. 



In Black River time that excellent datum plane — the Lowville 

 and its red sandy facies, the Moccasin or " Bays " — began a new 

 series of alternating tiltings in which the southern invasions pre- 

 dominated. The Lowville, itself, extends from the Mississippi River 

 far eastward to East Tennessee and in places there overlaps the 

 Chazyan formations quite to the edge of the overthrusted Lower 

 Cambrian formations. To the north in the middle stretch of the 

 valley the Chambersburg, which invaded from the northeast and 

 follows the Lowville, extends southwardly from Pennsylvania to 

 Lexington, Va., beyond which place it has not been recognized. 

 Usually, and perhaps throughout its extent, the Chambersburg is 

 succeeded by the shaly lower Martinsburg facies of the Trenton. 

 In the belt just within the Avestern side of the valley, in which 

 it is represented by its typical limestone facies, the Trenton is 

 succeeded by either the Reedsburg shale phase of the Cincinnatian 

 or by distinguishable Eden and Maysville formations. In the 



