1903] FLORA OF NORTH CAROLINA * 243 
these occupy deep narrow gorges. The broad valleys must have 
been formed at base level, before the commencement of the gorge 
cutting, and they afford the best possible evidence that the alti- 
tude of the region in which they are found has been increased by 
elevation in comparatively recent times. 
HYDROGRAPHY. 
The waters falling upon the several parts of this future 
National Park find their way eastward to the Atlantic, or south- 
ward directly to the Gulf of Mexico, or to the Mississippi River 
and thence to the Gulf. The divide between the Atlantic and 
Gulf drainage follows the crest of the Blue Ridge. The eastward- 
flowing streams are pressing this divide gradually westward by 
the capture of territory from less favorably situated streams west 
of the divide. Northwest of the divide the streams flow at first 
in the high broad valleys, then in deepening channels, directly 
to the higher, more rugged Unakas, which they cut through in 
narrow gorges, emerging upon the Appalachian Valley, those 
south of New River draining their waters into the Tennessee 
River? 
PHYSIOGRAPHY AND GEOLOGY. 
The history of this region, as far as it concerns this paper, 
begins with the Cretaceous period. At least two great cycles of 
erosion are recorded in the southern Appalachians, ‘in which the 
surface of an old continent was worn down from a considerable 
altitude nearly to base level. Shortly after the close of the 
Carboniferous period, the entire southern Appalachian province 
was finally lifted above sea level, and its subsequent history is 
recorded in the land forms. Following this uplift was a long 
period, during which the region was subjected to the physio- 
taphic processes constituting gradation. Finally, toward the 
close of the Cretaceous period, the whole province was reduced 
to a nearly featureless plain, the Cumberland peneplain, relieved 
2See Hydrography of the southern Appalachian Mountain region. Water Sup- 
ply and Irrigation Papers. U.S. Geolo ine Survey, nos. 62 and 63. 8vo, 190 pages. 
Washington, 1902. These two papers by Henry A. Pressey give systematic measure- 
ments of the streams in the southern rena Mountain district, and other data of 
‘Special interest to the ecologist. 
