March 15, 1007] 



SCIENCE 



429 



Chattahoochee and Savannah Rivers, and mol- 

 lusks of the Savannah drainage in the Chatta- 

 hoochee River. From this he was led to sup- 

 port the tlieory of a capture of the upper 

 Chattahoochee drainage by the Savannah 

 River, since the diversion in question would 

 effect the transferrence of fresh-water faunas 

 from one stream to the other. A paper on 

 'The Gaology of the Tallulah Gorge' CAm. 

 Geol., 1901), by Mr. S. P. Jones, discusses 

 the general geology of the region, mentions 

 the possibility of capture already suggested 

 by Hayes and Campbell, but reaches no con- 

 clusion in regard to the matter. Other refer- 

 ences to this capture are found in the litera- 

 ture, but need not be repeated here. 



Believing that the upper Savannah would 

 probably show evidence of river capture, and 

 desiring to make a test of certain principles 

 which had been applied in the ease of the 

 supposed capture of the upper Tennessee 

 River with only negative results, the writer 

 spent a month in the Tallulah district during 

 the spring of 1905, studying the geologic and 

 physiographic features of the district with 

 special reference to the supposed changes in 

 drainage. The evidence in favor of capture 

 appeared to be quite conclusive. A detailed 

 discussion of the various elements of the prob- 

 lem will be found in the Proceedings of the 

 Boston Society of Natural History, Vol. 33, 

 No. 5, but it is desired to outline certain 

 phases of the subject here. 



The results of this study appear to justify 

 the following conclusions: 



1. The upper Savannah (Chattooga) River 

 formerly flowed southwest through the Chatta- 

 hoochee River into the Gulf of Mexico, but 

 was diverted to the Atlantic drainage by a 

 process of stream capture, as already an- 

 nounced by Hayes and Campbell. 



2. The capture furnishes an example of 

 what may be termed ' remote capture,' having 

 occurred so long ago that much of the direct 

 evidence has been obliterated. 



3. The capture seems to have resulted from 

 the advantage gained by the Atlantic drainage 

 over the gulf drainage, owing to the shorter 

 course to the sea which streams of the former 



sj'stem enjoyed, although the process may 

 have been aided by crustal warping. 



4. The place of the capture was near the 

 junction of the Tallulah River with the Chat- 

 tooga, and probably just below that junction. 



5. The falls of the Tallulah River, while 

 initially caused by the capture, exist to-day 

 because of a hard rock barrier crossed by the 

 river, but not yet worn down by it. 



6. The similar falls which must have exist- 

 ed on the Chattooga River have been obliter- 

 ated by that stream, since the great lapse of 

 time since the capture has been ample for it 

 to grade its course in the less resistant rock 

 over which it runs. 



The Tallulah district is crossed from north- 

 east to southwest by the southwestern exten- 

 sion of the Blue Ridge escarpment, which is 

 from 500 to 600 feet high at this point. The 

 escarpment connects a higher with a lower 

 peneplain, both of which are eroded on folded 

 crystallines, the higher one sloping gently to- 

 ward the west, the lower one gently toward the 

 southeast. The streams on the higher level 

 flow in fairly mature valleys cut but slightly 

 below the general surface. In like manner 

 the streams on the lower level flow in broad 

 shallow valleys; but their upper branches are 

 working actively headward into the higher 

 level, thus pushing the escarpment backward 

 to the northwest, and capturing additional 

 drainage areas from the rivers flowing on the 

 surface well above them. 



In striking contrast to these two classes of 

 streams, on the lower and upper levels, respect- 

 ively, is a drainage system cut down into the 

 upper level. This is the upper Tugaloo-Chat- 

 tooga River, which flows in a deep gorge cut 

 500 feet or more below the upper level, until 

 it breaks from its gorge at the face of the 

 escarpment and flows out over the' lower level 

 in a fairly mature valley. Nothing could be 

 more striking than the contrast between this 

 young stream with its picturesque, steep-sided 

 chasm, cut in the upper level, and the mature 

 streams in broad open valleys flowing on the 

 upper and lower levels. The Tallulah River 

 flrst flows through low mountains on the upper 

 level, but when near its junction with the 

 Chattooga suddenly plunges down into a gorge 



