834 GEOLOGY 



drainage lines competent to fill the shallow valleys and spread 

 rather generally over the low divides of the coastal peneplain. In 

 the region of deeper valleys, such as the Tennessee, the valleys 

 were only partially filled. It has generally been assumed that the 

 formation was once continuous east of the mountains where patches 

 only now remain; but it may be that the higher divides, especially 

 toward the source of supply of the sediment, were never covered 

 by the formation. 



The removal and re-deposition of material in the manner 

 sketched above is regarded as an important part of the interpre- 

 tation of the formation, and the source of grave difficulty in the 

 correlation of it and its derivatives. The erosion and re-deposition 

 of the material did not cease with the Lafayette epoch, but has 

 been in progress ever since, and the derivatives so closely resemble 

 the parent formation in structure and material that their interpre- 

 tation is exceptionally difficult. 



If it shall ultimately be shown that the seaward portions of the 

 Lafayette, now concealed or unstudied, are marine, the preceding 

 hypothesis would need to be modified only by supposing that as 

 the feeding ground of the streams was bowed up, the coastal border 

 of the plain was submerged. In this case, there should have been 

 estuarine formations in the seaward valleys. 



The chief alternative view relative to the origin of this forma- 

 tion regards it as marine 1 , deposited during a stage of submergence 

 essentially co-extensive with the area of the formation. This 

 hypothesis has been faithfully applied by geologists of wide famil- 

 iarity with the phenomena, and abandoned as untenable even 

 where the conditions seem most to favor it. It is, however, still 

 entertained by others. The difficulties felt by those who have 

 abandoned it are (1) the absence of marine fossils; (2) the presence 

 of structural features not indicative of typical marine deposits; 

 (3) the chemical condition, particularly the high and very varying 

 oxidation, and the meager hydration; (4) the topographic relations 

 of the formations, especially the lack of any approach to horizon- 

 tality of its upper limit; and (5) the absence of shore phenomena. 

 The terraces and cliffs that have been appealed to in this connection, 



1 McGee, 12th Ann. Kept., U. S. Geol. Surv. 



