466 E. O. ULRTCH CORRELATION OF THE STRAND-LINE 



According to the conception above outlined, the Archeeopteris flora may 

 be properly designated as the late Devonian-early Mississippian flora. 

 The late Devonian part of its existence perhaps is distinguishable from 

 the early Mississippian part by peculiarities of relatively small biological 

 significance, but the facies in general is transitional in its time relations 

 and in its most typical expression intersystemic. It follows, then, that 

 the determination of the age of the Chattanooga and Ohio shales as De- 

 vonian or Mississippian can not be made on the basis of generalized floral 

 relations. Nothing less than absolute identity of species and varieties 

 should be accepted as competent criteria in this case. Preponderance of 

 Devonian affinities should not of itself be regarded as decisive, because it 

 may readily prove more apparent than real. The true time relations of 

 that part of the durance of the intersystemic floral concept which suc- 

 ceeded the diastrophically marked boundary between the two systems by 

 so much as the late Devonian part preceded it may not have been recog- 

 nized. I believe, indeed, that this has happened in the case of the Ohio 

 and Chattanooga shales. These plant-bearing eastern representatives* of 

 the Kinderhook have been determined as Upper Devonian on the basis of 

 apparent preponderance of floral affinities, this mistaken interpretation 

 being still more fastened on us by the prevailing erroneous assumption of 

 a Kinderhook age for the Pocono of the Allegheny region and for the 

 Cuyahoga of Ohio and Kentucky. Both of these formations (the Pocono 

 and Cuyahoga) seem to me of approximately the age of the Culm of 

 Europe and all three as post-Kinderhook. Under this interpretation the 

 land flora of Kinderhook age should be much more like the Upper De- 

 vonian flora than is that of the second Mississippian epoch, which is rep- 

 resented in America in the Pocono and in Europe in the Culm. The 

 Chattanoogan being, as I think, of Kinderhook age, its flora may then be 

 expected to be closely akin to the Upper Devonian flora ; and its true age 

 is indicated less by preponderance of affinities than by the few first ap- 

 pearances of types marking the succeeding epochs. 



Finally, in correlating minor zones of the late Devonian-early Missis- 

 sippian floral or faunal sequence, nothing less than absolute identity of 

 species and varieties should be accepted as determinative. 



Revised Methods and Principles of Correlation and 

 Classification 



general discussion 



So long as our leaders are expected to deliver opinions, errors of judg- 

 ment and the confusion incident to correction and readjustment to accu- 



