Appalachian Geosyncline. 229 



antedate the chief period of mountain building. Successive 

 periods of orogenic activity seem in general to extend and weld 

 together axes of movement which were previously more or 

 less separate. A mountain barrier in the Upper Devonian 

 in this region is therefore not evidence against a transverse 

 strait in the late Silurian provided the faunas of the latter period 

 indicate its probability. 



In regard to the Hamilton epoch of the Middle Devonian, 

 an Atlantic passage should be looked for however rather to 

 the south of New Jersey, or else along the northwestern side 

 of the Saint Lawrence axis. It is seen that there is no positive 

 evidence as to either connection ; the southern seaway would 

 be the shorter to the present ocean, but in the latter part of 

 this paper the evidence is presented which suggests that 

 Appalachia was of considerable breadth and the Devonian 

 Atlantic was not so near. Furthermore in the Upper Devo- 

 nian the sedimentary evidence is more positive that marine con- 

 nections could not have existed north of Virginia, probably not 

 north of North Carolina. 



This problem of the relationships of the fauna of the Che- 

 mung sea and its connection with the Atlantic province is 

 really not a vital part of the problem of the Upper Devonian 

 delta and may be left in this indeterminate state. It has been 

 dealt with so far as it is necessary to show that other connec- 

 tions could possibly have existed besides that which has been 

 postulated as crossing New Jersey. The latter seems clearly 

 disproved by the whole assemblage of evidence, and it is seen 

 that an easier line of ingress may be conceived along the north- 

 western side of the Appalachian deltas. 



Character of the Sediments of the Marginal Outcrops. 



Where the edges of the upturned folds show strata many 

 thousands of feet in thickness as in Pennsylvania, or where 

 almost similar thicknesses of nearly horizontal beds remain in 

 mountains of circumdenudation, as in the Catskills of New York, 

 it is clear that in most cases the formations must have thinned 

 out gradually beyond their present limits. The only exception 

 is found on the borders of fault troughs. There a continual 

 raising of the walls and a simultaneous settling of the basin 

 permits a deep filling of debris at the very base of the block 

 mountains. Such a condition records its evidence if the for- 

 mations are of continental nature, by talus conglomerates and 

 alluvial fans. If the fault movements are principally of pro- 

 found subsidence rather than of uplift, as around the present- 

 day shores of Greece, wave-formed conglomerates may be ex- 

 pected to mark the presence of the shores, passing outward 

 rapidly into comparatively deep-sea deposits. In the formations 



