NO. 2.] SNAILS OF THE GENUS 10— ADAMS. 47 



more or less longitudinal axes of uplifts, also indicated on plate 56. The axis O P extends in a 

 north and south direction; E F and G H are longitudinal with the Appalachians. Still another 

 longitudinal axis crosses the Kanawha, and is indicated C D. The evidence for these axes is 

 determined by the present altitudes of the deformed and tilted remnants of the Cretaceous 

 peneplain, and clearly indicate that the greatest elevation of the peneplain is toward New 

 River. As stated by Hayes and Campbell ('94, p. 93) : 



This is in northern Virginia and West Virginia and * * * exhibits an aggregate uplift since the completion of 

 the Cretaceous peneplain of 4, 000 feet. During the Tertiary base-leveling this region was necessarily free from move- 

 ment, but at no other time does there seem to have been a complete cessation of the uplift. The axes along which it 

 culminated in pre-Tertiary time are C D and E F. [Cf. pi. 56.] 



While thus the highest parts of the Appalachians are in the south, this is mainly because 

 of the unreduced Cretaceous areas upon that peneplain rather than the post-Cretaceous uplift 

 of this peneplaia. Thus two slopes were produced, one from the southern mountains and the 

 other a southwestward tilting from New River. Such a tendency to uplift the divides must 

 have favored large axial streams in the intervening region. The position of the Memphis- 

 Charleston axis crossing the lower Appalachian VaUey was probably the factor which has 

 prevented the formation of a large Appalachian VaUey axial stream. (PI. 56.) Keith ('96), 

 on the other hand, is inclined to consider that the influence of local axes has been overestimated 

 in the study of this region. He is inclined (pp. 521-522) to attribute the present variation in 

 the altitudes of the different fragments of ancient peneplains more to the local conditions under 

 which they were formed than to differential uplifts. Thus distance from the sea and character 

 of stream debris will influence the formation of more or less local base-levels of erosion. He 

 says: 



It is to be expected, therefore, that widely dissimilar basins will have peneplains formed at the same time, but 

 at somewhat different altitudes. Such expectation is amply borne out by the facts of the field, and is in fact exceeded. 

 The least inspection of peneplains shows differences of altitude amounting to 3,000 feet. Two explanations can be 

 made of such great differences, either that one or two peneplains have been warped out of their original plane, or that 

 many peneplains are represented which were produced at different periods and successively elevated with little warping. 



The conditions in the early Tertiary therefore appear to have been: An uplifted, deformed 

 Cretaceous peneplaia, with transverse Appalachian Valley drainage; drainage slopes from 

 New River to the southwest and from the higher mountains; uplift along both transversely 

 bounding axes and more or less longitudinal ones, the gieatest uplift being to the north, or 

 there may have been an uplift with little warping. With these conditions and an abundant 

 raiofaU and diverse rock structure the present topographic features and drainage of the South- 

 ern Appalachians have been developed. With the exception of the highest parts of the Southern 

 Appalachians and other Cretaceous relicts these general conditions are duplicated in part in the 

 mountains of Pennsylvania; as expressed by Davis ('91, p. 583): 



They are essentially the products of Tertiary erosion on an uplifted Cretaceous peneplain of moderate reKef . The 

 pre-Cretaceous forms are in nearly all parts lost; the post-Tertiary work is in nearly all places insignificant. Our 

 topography is, for the most part, a Tertiary product. 



And this woiild also be true, in a measure, even to-day, of the drainage and the major habi- 

 tats and environments, which are dependent upon the topography in the Southern Appalachian 

 region, had it not been for a later baselevel which was first clearly recognized by Keith. This 

 plane will be considered later. 



The Tertiary period was one of tension, for as the uplift advanced erosion progressed; 

 but as soon as the uplift ceased, a period of partial equilibrium was initiated as erosion developed 

 the peneplain. But that the duration of this period of stability was not as long as that during 

 which the Cretaceous peneplaia was formed is clearly shown by the fact that only the less resist- 

 ant rocks were reduced, and the harder ones have remained as unakas and monadnocks and 

 have formed large interstream areas, as shown in plate 58. The softer rocks of the Appalachian 

 Valley eroded rapidly and the valley continued to develop and to become a more and more 

 marked topographic feature of the region. The differences, due to rock structure and differential 

 erosion, which were relatively latent upon the peneplain, now became more and more promi- 



17829°— 15 4 



