OSCILLATIONS RECORDED IN STRUCTURE. 59 



parts of the province, through strong- warping of the earthcrust, from 

 only about 100 feet to more than 700 feet; yet the entire record is essen- 

 tially one of vertical movement alone. A still more remote record is 

 found in the C'olumbia-Lafiiyette unconformity, which i)roves that the 

 land rose unequally, in a part of the province only a little over a hun- 

 dred feet, in other parts several hundred feet, and in one })art nearly or 

 quite a thousand feet higher than now; yet there is no record of hori- 

 zontal movement connected with this wide vertical oscillation. Still 

 earlier episodes are recorded in numbers; yet all records are essentially 

 alike — all indicate vertical movement through hundreds of feet, all indi- 

 cate that the earthcrust war])ed so that the movement varied from place 

 to place, all fail utterly to indicate appreciable horizontal movement. 

 Moreover, in this province of highly significant geologic records the ver- 

 tical movements of the later half of geologic time fall into rhythmic series 

 of oscillations, each beginning strong and gradually dying out, while at 

 the same time the best known warpings fall into a definite S3^stem in 

 which the axes of relative stability and of maximum movement persisted 

 through several successive episodes ; and this impressive harmon}^ of 

 vertical movement expresses a formal if not a l)h3^sical laAv of epeirogeny 

 in which lateral movement plays no part. Still further, the movements 

 extended beyond the limits of the province and are now known to rep- 

 resent a system of vertical undulations affecting all of southeastern 

 United States.^ 



The formations and unconformities of the American coastal plain give 

 but an instance which might be repeated, albeit less completely, along 

 the coastal zones of other continents, and the testimony of all the coastal 

 zones of the world is alike — all tell of vertical oscillation, none tell of 

 commensurate horizontal movement in the earthcrust. The formations 

 and unconformities are interpreted by direct inference, by inference in 



♦These movements htive been summarized elsewhere (Compte-Rendu du Congrf»s G6ologiqne 

 Internutioriiil :"i Washington en 1801 (18y4), p. Kir)), ,ih follows: "In general the post-Jurassic his- 

 tory of the subcontinent represented by southeastern United States is one of progressive uplift 

 along the Appalachian axis, progressive downthrow about the peripiicry (extending from the 

 Atlantic coast through tiie (iulf of Mexico and some distance northward in the Mississip])! valley), 

 with concomitant seaward tilting of the Piedmont areas, 'i'hc movement was not uniform, but 

 spasmodic. Each tiiroe was complex, including an initial warping and a series of os(;illatioiis. 

 The first movement in each throe was (a) relative uplift of the Appalachian axis and downthrow 

 of the periphery, coupled with {h) depression of the entire area perhaps to such an extent as to 

 counterbalance the axial uplift, thereby (c) submerging a considerable part of the subcontinent 

 and ('/) stimulating degradation over the interior. The second movement in each throe was g«'n- 

 eral elevation, without recognized tilting, followed by gradual subsidence, and, in some cases at 

 least, a diminishing series of minor oscillations. The subsidence and elevation of each throe 

 were coonlinatc, profound subsiden<'e being followed by high elevatir)n; limited subsidence by 

 slight elevation. This law of continental movement, which is singularly simple and rhythmic, is 

 apparently excn)plificd in all of the oscillations in wiiicii the coastal plain and the contiguous land 

 area have participated." 



9 



