LARGER RELATIONS 0]<^ DELTAS 409 



"toward the close of Jurjissic time and at the opeiiiuj^ of the succeedinj^ 

 period — the Cretaceous — estiiarine conditions are known to have prevailed. 

 About the middle of Cretaceous time the barrier between the Dela- 

 ware estuary and the sea disappeared and the Paleozoic crystallines bearing; a 

 cover of early Cretaceous deposits were sul)merf;ed beneath the Atlantic." 



In the statements as .to the mode of origin of these formations there 

 has thus far been no pi'o and con discussion as to the possibility of a 

 terrestrial and fiuviatile as opposed to an estuarine and subaqueous ori- 

 gin. Rather the assumption of earlier times as to the accumulation of 

 all sediment in bodies of standing water has been carried forward to the 

 present. That of lacustrine origin has apparently been ruled out by the 

 gradation which occurs in the Upper Cretaceous from fresh water into 

 truly marine formations. The assumed existence of a land barrier lying 

 to the east of the ^^resent Coastal Plain rests merely on tlie initial hy- 

 pothesis of an estuary from which the sea must be barred save at the 

 mouth. 



As defined in standard works on the English language^ an estuary is 

 that part of the mouth or lower course of a river flowing into the sea 

 which is subject to tides, and as argued in a previous section is the result 

 of a recent marginal subsidence aifecting lands of considerable relief. 

 The late Mesozoic deposits of the Atlantic coast in contrast to these con- 

 ditions began to be deposited on a fairly developed peneplain. The 

 formations outcrop parallel to the Appalachian system from Massachu- 

 setts to the Mississippi A'alley and are thicker toward the sea, giving no 

 hint of a barrier to the southeast, but indicating rather that subsidence 

 of the coast was accompanied by upwarp of the interior. These for- 

 mations, furthermore, according to all observers, give evidence of shallow 

 waters, with an absence of marine faunas througli late Jurassic and 

 LoAver Cretaceous time. They were deposited therefore not in drowned 

 valleys radiating away from the mountains, but as a marginal fringe, 

 where the old land was depressed below baselevel. There is none of the 

 physiographic setting of estuarine conditions. On the contrary, terres- 

 trial and fluviatile deposition is suggested by the follow^ing features: 

 The individual strata are markedly discontinuous, beds and lenses of clay 

 and gravel occurring in sandstone and vice versa. Highly variegated 

 clays are abundant, in which the state of the^iron oxide varies from 

 stratum to stratum and laterally through the same stratum, indicating 

 varying facilities for oxidation, both vertically and laterally. Segrega- 

 tions of iron ore are abundant at many horizons, and the writer lias noted 

 the patterns of shrinkage cracks in certain of. the plates of ore. The 

 abundant leaf impression, the lignitized and silicified wood, and the ap- 

 XXX — Bull. Geol. Soc. Am., Vol. 23, 1911 



