Subterranean Phenomena ZOG. 
through an underground system which has its terminus at Blue Spring. 
(See Fig. 2.) Blue Spring is a spring of great volume which rises 
out of a cavernous opening at the foot of the rocky meander curve in 
section 16, and enters Indian Creek channel. Little of the cavernous 
opening is visible, as the spring is artesian. After heavy rains the 
muddy waters rise vigorously and in greatly increased volume. During 
dry weather the pool at the opening is a deep blue color, and the water 
rises quietly and flows away at one side practically at the level of 
Indian Creek. 
Possum Valley is characteristic of many valleys of its kind devel- 
oped in the Mitchell limestone along the western margin of its outcrop. 
Such valleys are almost invariably tributaries to a larger and more 
deeply intrenched main stream. They have originated as valley basins 
through normal surface erosion in the clastic rocks of the Chester 
series. As the main streams were intrenched through downward ero- 
sion, the tribuary valleys were also cut down, but less rapidly than 
the main streams. When the tributary streams had cut through the 
clastic rocks to the Mitchell limestone, the main streams were already 
well intrenched within the Mitchell limestone. The _ tributary 
streams were thus somewhat perched above the main streams, and 
possessed a valley floor of limestone. Subterranean drainage gradually 
developed in the tributary valleys, especially at some distance from 
their junction with the main streams. In many cases the waters which 
enter the subterranean channels through the swallow-holes in the mid- 
dle and upper portions of the near streamless valleys re-enter the 
valley at the surface and continue to the main stream as a surface 
stream. But more frequently the waters have been diverted through 
subterranean channels directly to the main stream, the waters passing 
beneath the divide between the main stream and the tributary. Beaver 
Valley west of Mitchell in southern Lawrence County is an example of 
semi-streamless in its upper portion, the subterranean waters of which 
in part come to the surface lower down in the valley basin. Possum 
Valley illustrates the sort in which the water has been diverted by sub- 
terranean piracy. 
It should be noted that there is a distinct difference in the manner 
of stream diversion in subterranean stream diversion as compared to 
surface stream diversion. In the latter kinds of stream diversion the 
diverting or pirate stream is the sole aggressor, while the diverted or 
captured stream is wholly passive. In the case of stream diversion 
through the development of subterranean drainage, the diverted stream 
is the chief aggressor and brings about its own diversion. Because 
of such a fundamental difference in the manner of stream diversion, 
some question arises in the mind of the writer as to the propriety of 
calling subterranean stream diversion stream piracy, though the ex- 
pression stream diversion conveys the full meaning of the action. 
Subterranean drainage takes place as a matter of economy of dis- 
tance. The subterranean routes are always shorter and more direct 
than the abandoned surface routes. In the case of Possum Valley the 
economy of distance is obvious. The subterranean route under the 
dividing ridge is very short as compared to the old surface route below, 
