JOHNSON: TALLULAH DISTRICT. 
245 
nearly or quite completed before an actual surface-valley connection 
was formed, since, as Lane (’ 99 , p. 12) has pointed out, leakage 
through the rocks from the higher to the lower level will go on for a 
long time, possibly increasing until all of the water from the higher 
level passes underground to the lower stream, leaving a dry channel 
below the point of capture to the first water found in the shrunken, 
beheaded stream. Under these circumstances there could be no possi¬ 
ble transfer of faunas dependent on direct freshwater communication. 
On the other hand, there are so many other means for the dispersal 
of freshwater shells, and the evidence in other localities is so conclu¬ 
sive that they have been dispersed by such means, that we may reason¬ 
ably suppose shells from either of the two systems might be trans¬ 
ferred to the other independently of the capture. For this reason 
I do not believe the distribution of the shells can be urged as proof 
of capture, although the fact of capture is well attested by other lines 
of evidence. 
Alternative Theories. 
Instead of capture of the upper Chattahoochee by the upper Savan¬ 
nah, we may suppose that the streams have always had their present 
relations. On the basis of this supposition it is difficult to account 
for the systematic relation of the topographic features, or the presence 
of river gravels in the area between the peculiar elbow bend and the 
head of Deep Creek. That one branch of the Tugaloo system should 
have eaten headward through the escarpment and developed a large 
tributary running well up into the mountains to the northwest, and 
another running northeast well into North Carolina, together with a 
large series of other tributaries, while in the same time similar branches, 
apparently little less favored, should only be able to make small notches 
in the face of the escarpment, seems quite unreasonable. Neither 
should we expect a considerable river system such as the Tallulah, 
to be developed by gradual headward erosion and branching and still 
preserve extensive falls on its lower course. Such falls might be the 
result of rejuvenation due to general uplift, but while all the streams 
of this district are cutting down to a lower level in an uplifted pene¬ 
plain, the falls on the Tallulah cannot be correlated with other features 
due to that uplift, and evidently have an independent origin. Mr. Jones 
has suggested some local earth movements, affecting the lower Tallu- 
