110 
John R. Holsinger and David C. Culver 
New and Roanoke rivers on the south. The regional terrain varies con- 
siderably from one part of the basin to another. In the western two- 
thirds it is relatively rugged and characterized by numerous prominent 
ridges and narrow valleys, whereas in the eastern third it is of lower 
relief and generally rolling. 
A total of 431 caves are recorded, including some of the largest in 
the study area. There are significant exposures of Silurian and Devo- 
nian limestones in the western part of the basin, where caves are often 
extensive but frequently localized in isolated belts of limestone that crop 
out along the flanks of ridges and in valley floors. Limestones and 
dolomites of Cambrian and Ordovician age predominate in the eastern 
part of the basin, where caves are less extensive but relatively numerous. 
The regional cavernicolous fauna is composed of 32 cave-limited spe- 
cies; 31 are troglobites, and 16 are endemic to the basin (Table 6). 
3. Roanoke Basin . — This faunal unit is the smallest in the study 
area and covers only approximately 1073 km (Fig. 2). It is drained by 
the Roanoke River and its tributaries and is defined by the Blue Ridge 
Mountains on the east and south, Brush and Catawba mountains in 
part on the north, and a drainage divide (with carbonate rock) with the 
New River on the west. Although the regional terrain varies considera- 
bly, most of the karst topography is moderately rolling and developed 
on valley floors and low hills. Ninety-one caves are recorded, and all of 
them are developed in Cambrian and Ordovician limestones and dolo- 
mites. Because of the extensive exposures of dolomite, most of the caves 
are small, although several large ones are excavated in Ordovician 
limestone in the valley of the North Fork of the Roanoke River. The 
regional cavernicolous fauna consists of only 10 cave-limited species, all 
trogobites; three species are endemic to the basin (Table 7). 
4. New Basin . — This faunal unit encompasses that part of the 
study area drained by the New River and its tributaries and covers 
approximately 4087 km (Fig. 2). Unlike other major rivers in the study 
area, New River flows generally northward and cuts across the regional 
strike instead of flowing parallel to it. The basin is defined by the Iron 
Mountains and by Poplar Camp and Macks mountains on the south, 
complex drainage divides with the Roanoke and James rivers composed 
of several ridges of prominent relief on the east, Peters and East River 
mountains and Big Stone Ridge on the north, and complex drainage 
divides (partly composed of carbonate rocks) with the Holston and 
Clinch rivers on the west. The regional terrain is heterogeneous and 
characterized in general by both broad and narrow valleys and a 
number of prominent ridges. 
A total of 419 caves are recorded, a significant number of which are 
extensive. Both caves and karst terranes occur in many parts of the 
basin but are especially well developed in large valleys on opposite sides 
of Cloyds and Brush mountains, along the western side of Big Walker 
