442 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF XORTH AMERICA 



the presence of the sea might have no pronounced influence on the cli- 

 matic conditions over the adjoining slopes of the Appalachian old land, 

 such climatic conditions being determined by wholly distinct causes. 

 That such periodic elevation of the old land might have taken place can 

 not be denied. Indeed, the probability of repeated elevations is sug- 

 gested by the fact that a pronounced deformation, with intense folding 

 and faulting, brought the Ordovicic period to an end. Such successive 

 risings might be considered preliminary movements, which culminated 

 in the great Taconic Mountain revolution. 



The conditions most favorable for the formation of these late Ordo- 

 vicic continental deposits are shown in the following diagram (figure 5), 



Figure 5. — Hypothetical Sections across Faleozcic Appalachia 

 Showing the deposits which would result if the prevailing winds were easterlies 



but it must be borne in mind that this is only one possible explanation, 

 and that it apparently involves the recognition of a wholly different posi- 

 tion for the earth's axis from the existing one. There may be other ex- 

 planations, but I can not help thinking that in view of the succession of 

 such deposits which, as will be shown in this and subsequent papers, are 

 repeated four times in the Appalachian region, none can be so satisfying 

 or can so completely account for all the phenomena observed. The full 

 significance of such an arrangement and the possibility of its having 

 occurred will be discussed in a subsequent paper.* 



PROBABLE EXTENT OF FOLDING OF THE STRATA AXD SUBSEQUENT EROSION 



General discussion. — As is well known, Ordovicic sedimentation was 

 followed by a folding of the strata in the eastern part of Xorth America. 

 That this folding of the Ordovicic strata was in pre-Shawangunk time is 

 indicated by the striking unconformity everywhere found between this 

 rock and the Hudson series on which it rests. That it occurred long 

 before the deposition of the Shawangunk, the age of which is basal 

 Salina (basal mid-Siluric), is shown by the very pronounced character 

 of the unconformity, and by the extensive erosion which the lower beds 



* For a discussion of the "Pendulations-theorie," and the general orohlem of the shift- 

 ing of the earth's axis, see Principles of Stratigraphy, chapter xxiii. 



