240 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
finally capturing the headwaters of C 3 . The inverted stream is 
beginning to notch the wall of the gorge at X. 
The last figure, (fig. 9), represents the conditions a long time after 
capture. The falls on the main stream A have been so thoroughly 
graded that only minor rapids are to be found. 
In the hard rocks across which it runs, B has not yet been able 
to grade its course, and the falls still persist, being worn back only 
to Z 1 . For the same reason the gorge below the falls remains deep 
and narrow, whereas A has widened its valley to a greater extent in 
the softer rocks, entirely consuming all evidence of the former valley 
floor, such as the terraces or benches seen in figure 8. Even the 
smaller tributaries on the soft rocks, C 1 , have worn their falls 
back .to a considerable extent, but the very smallest ones, G 1 , G 2 , 
have only been able to notch the valley walls slightly, and still exist 
as hanging valleys. The tributary F has grown so extensively as to 
have robbed much of the drainage area of A 1 , and prevented further 
growth of the inverted stream south of X, while all streams have dis¬ 
sected the upland surface to a much greater extent than before. So 
great a lapse of time has resulted in perfect adjustment in the drainage 
of A 1 , and we no longer find alluvial fans, or pronounced meandering 
in an inappropriate valley. Maturity of development characterizes 
the streams of this upland area, but more youthful features still mark 
the streams of the other system. In the younger portions of F there 
may even be numerous falls not yet worn down to grade, while rapids 
are to be found along all the streams of this system. The conditions 
are typical of what might be termed “remote capture.” 
Much later even than this period, at a time when the capture might 
be termed “extremely ancient,” the falls on all the streams will be 
graded, the gorges widened out to mature valleys, the interstream 
areas much dissected and subdued; even the smallest tributaries will 
enter their mains at accordant levels, and practically all the evidence 
of the capture will have disappeared, except the peculiar elbow bend 
in the main stream, produced by that capture. The drainage pat¬ 
tern alone will remain to suggest an important chapter in the history 
of the stream’s development, and even that evidence may suffer exten¬ 
sive modification in time. 
