National Geographic : 1894 May 23
110 Hayes and Campbell-AppalachianGeomorphology. It should be remarked that while the writers formerly regarded the character of the divides between these drainage basins as conclusive evidence that large streams flowed across them until the close of the Tertiary period of baseleveling, they have recently found reasons for modifying this conclusion. A study of the divides between drainage basins throughout the Appalachian valley from Pennsylvania southward shows that most of them are quite perfectly reduced to the altitude of the Tertiary pene plain in adjacent basins, although not generally so broadly cut as the one in question. There is no reason, so far as known, for supposing that the divides between the Potomac and James or the James and Roanoke basins have shifted during the Tertiary cycle, yet they are nearly as inconspicuous as those between the Tennessee and Coosa. On the other hand, the divide between the New and Holston basins has the form of a narrow col, such as would be expected to characterize all long-maintained divides. Evidencefrom the Volume of Materialeroded and deposited.-The second line of evidence bearing on the date at which the Appa lachian drainage was diverted to its present westward course is derived from a comparison of the volumes of Tertiary erosion and Tertiary sediments. It is comparatively easy to compute the volume of the material which was removed by the rivers during the Tertiary cycle, when the vertical distance between the previously existing peneplain and the one developed during the Tertiary cycle is known, together with their lateral extent; also a tolerably safe estimate may be made of the volume of sediments deposited by each of the rivers during the Tertiary cycle. If the drainage during the whole of the cycle was essen tially as it is at present, then the volume of sediments which would naturally be deposited by the present streams and the volume of the material eroded by those streams should show a practical agreement. The formations laid down during the Ter tiary cycle are regarded as including (1) the Ripley-sands and sandy clays overlying the Rotten limestone and marking the uplift which terminated the preceding cycle; (2) Lignitic; (3) Buhrstone; (4) Claiborne; (5) White limestone *-a series de creasing in coarseness and increasing in amount of calcareous * The Tertiary and Cretaceous Strata of the Tuscaloosa, Tombigbee and Alabama Rivers, by Eugene A. Smith and Lawrence C. Johnson : U. S. Geological Survey, Washington, Bull. 43, 1887, 189 pp., 21 pls.
1894 Jun 22
1894 Apr 25