STRAND-LINE DISPLACEMENTS 493 



in the Oriskany, as shown by the absence of Upper Oriskany and Onon- 

 daga deposits in the southern Appalachian sea. In Marcellus time the 

 northern area, of this same sea again began to spread southward, reaching 

 southern Kentucky, and then extending across the Cincinnati axis into 

 the Indiana basin. South of Kentucky the Appalachian trough was land, 

 and thus remained throughout the Upper Devonic. This uplift does not 

 appear to have been a marked one, however, certainly not for the south- 

 ern half of Appalachia, for the clastic material of the adjoining seas, 

 which were of late Devonic and early Mississippi times, consists of black 

 shales of a very fine texture. During the Middle Devonic, Acadia was 

 repeatedly subjected to tangential movement, and this area has furnished 

 the major amount of the vast clastic material of the late, Middle, and 

 Upper Devonic formations of the northern Appalachian trough. Never- 

 theless, throughout the period of these secular movements the Atlantic at 

 different times crossed northern Appalachia and distributed its faunas in 

 the New York basin. 



It is evident, therefore, that the Chemung emergence was more specific- 

 ally a condition of the Atlantic border, and that it became even more 

 marked in the Mississippic period. It of course decidedly affected the 

 areal distribution of the Appalachian, Saint Lawrence, and Mississippian 

 seas, but the Cordilleran and Sonoran seas continued with but little 

 physical change into the succeeding period. As the Cordilleran and 

 Mississippian seas may have remained in continuous communication from 

 the late Hamilton, the faunas of the latter sea have much the same aspect 

 as those of the former throughout Upper Devonic time. In the early 

 Mississippic the Kankakee axis was somewhat accentuated, and for a 

 time kept the Cordilleran and Mississippian seas apart. It was this bar- 

 rier, together with the changes in Acadia and Appalachia, and some with- 

 drawal of the continental waters, that caused the more decided faunal 

 changes in the eastern seas. In the western or Cordilleran sea, however, 

 there was a less decided faunal change at the close of the Devonic. In 

 other words, the diastrophism at the conclusion of the Devonic does not 

 appear to have been marked in character, as the emergence recorded in 

 the map (plate 77) was but 2 per cent smaller than that of the late Ham- 

 ilton. But a greater emergence took place at the very close of the De- 

 vonic, and may have decreased the area of the Middle Devonic by from 

 9 to 15 per cent; this difference, however, was sufficient to change the 

 faunas. In this instance the life record is thought to have greater value 

 than the physical one in separating the Devonic from the Mississippic, 

 but should the principle of diastrophism be the sole guide, then these two 

 periods seemingly must be combined into one. 



