44 JOURNAIv OF THE 



Island Sound, but gradually departing- therefrom to- 

 ward the south. In Maryland the departure amounts 

 to one hundred miles inland from the present coast and 

 it continues at about that distance to Georg-ia, where 

 it swing's rapidly westward and northward forming- the 

 Mississippi embayment of the Cretacous ocean. 



The extensive denudation, which had been long-g-oing- 

 on over the permanent land area, now extended over 

 those Triassic rocks which were above sea level, and, 

 by the beg-inning- of Cretaceous time, this area was re- 

 duced to surface of low relief, much as it appears to- 

 day, but somewhat nearer base-level. Of the condi- 

 tions existing- during- Jurassic time we know nothing- 

 since we have no distinctly Jurassic rocks in this prov- 

 ince. But of Cretaceous deposition we have a g-ood 

 record in at least two formations whose inland exten- 

 sion is marked by the Cretaceous shore-line already 

 described. 



A study of the earlier of these two formations by 

 W. J. McGee shows that, after the base-levelling- of 

 the ancient land area, which was achieved just before 

 Cretaceous times, a shoreward tilting* of the area took 

 place by which the streams were revived to such a de- 

 gree that they rapidly sank into deep narrow valleys. 

 A submerg-ence then caused the sea to invade these 

 estuaries, the coast assuming- in g-eneral the position 

 which marks probably the g-reatest transg-ression dur- 

 ing- Cretaceous time. Then followed the accumulation 

 of the Potomac sediments which, with their equivalents, 

 extend from New Jersey southward, certainly as far as 

 North Carolina, and probably as far as the Mississippi 

 embayment. A period of emerg-ences and retreat of 

 shore-line then intervened before the deposition of the 

 g-lauconite beds of later Cretaceous which are seen to 



