244 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
I can account for the occurrence of these gravels on no other basis 
than the theory of capture so strongly supported by the topographic 
evidence. It seems certain that the gravels along the former course 
of the Chattooga have been removed from their initial position by 
the extensive erosion since the remote date of the capture, and were 
carried down into the present valleys where they are occasionally 
found in favorable localities. 
On the supposition that these gravels would not be found north¬ 
west of the former course of the Chattooga (although they might be 
carried down-stream to the southeast any distance) the distribution 
of the gravels leads me to believe that the point of capture was just 
below the mouth of the Tallulah and that the former course was 
from that point strongly west and then southwest to the head of Deep 
Creek. 
Evidence of the Shells. 
As noted in the review of the literature, the theory of capture has 
been supported on the basis of certain facts in the distribution of 
freshwater faunas. It appears that a few shells from the Chatta¬ 
hoochee and more western drainage basins are found in the Savannah 
River, while a number of forms from the Savannah system are found 
in the Chattahoochee system. It is argued that these forms must 
have passed between the two systems at the time of capture. 
That the fauna of the upper Chattahoochee (the Chattooga River), 
might be transferred into the Savannah River by the capture would 
appear quite clear. It is much more difficult to account for the trans¬ 
fer in the opposite direction, however, if we limit ourselves to river 
capture as the means. Yet the main transfer is supposed to have 
been in that direction. That shells could have passed from the lower 
level of the Tugaloo up 500 or 600 feet over falls and rapids to the 
higher level of the Chattahoochee, does not seem probable. It is 
possible, of course, that the headwater portion of the capturing stream 
may have been a gradual slope instead of a series of falls, but the 
evidence of other streams working headward into the Chattooga 
escarpment suggests that the capture most probably was initiated 
by a series of more or less prominent cataracts. These would effec¬ 
tually prevent transfer through the water itself. Furthermore, there 
is good reason to believe that the transfer of water may have been 
