THE PLIOCENE PERIOD. 305 



Sucarnoche of Alabama, Flatwoods of Mississippi). These belts are 

 now rather lower than their surroundings, and the absence of the 

 Lafayette from them has usually been assigned to subsequent erosion. 

 An alternative interpretation, however, seems possible, in the light of 

 present knowledge. The areas from which the Lafayette is absent are 

 mainly underlain by calcareous formations. If they were divides when 

 the Lafayette was deposited, and if in later time they have suffered 

 more by solution than adjacent formations have by erosion, the present 

 relations might have been brought about. 



Fossils. — Fossils are rare in the known parts of the formation. 

 In the unquestioned and representative portions of the Lafayette, 

 all are of land plants and animals (except, of course, the fossils derived 

 from earlier formations). The formation is much dissected and un- 

 usually open to observation, so that the observed rarity of fossils must 

 be taken as really representative. As already remarked, it is probable 

 that seaward equivalents of the Lafayette contain marine fossils. 



Genesis. — As here interpreted, the Lafayette formation belongs 

 to an important class, long neglected, but now coming into recognition, 

 whose distinctive features are less critically familiar than those of 

 marine, lacustrine, and typical fluviatile formations. The preferred 

 interpretation is as follows: After the Cretaceous base-leveling of the 

 region, brought out by Davis, 1 Hayes, 2 Campbell, and others, the Appa- 

 lachian tract was bowed up and a new stage of degradation inaugu- 

 rated. During the long Eocene period, a partial peneplaning of 

 the less resistant tracts was accomplished. This was slightly inter- 

 rupted by the Oligocence deformation, and the streams mildly reju- 

 venated in the more responsive tracts. During the Miocene period, 

 base-leveling was resumed, abetted by relative subsidence along shore, 

 as indicated by the landward spread of the Miocene sea, and the open 

 low-grade valleys and abundant low cols of the region west of the 

 Appalachians, if the interpretation here given be correct. At the 

 opening of the Pliocene, therefore, the Appalachian tract is supposed 

 to have been affected by broad, flat, intermontane valleys, mantled 

 by a deep layer of residual decomposition products. The Piedmont 



1 Rivers of Pennsylvania and Geographic Development of Northern New Jersey, 

 Nat. Geog. Mag., Vol. I and Vol. II, respectively. 



2 Hayes, chapter on south Appalachians, in Physiography of the U. S. and 19th 

 Ann. Rept. U. S. Geol. Surv., Pt. II; Hayes and Campbell, Nat. Geog. Mag., Vol. VI. 



