1892.] 
419 
[Davis. 
late, and thus to throw much doubt on the assumption concern- 
ing the original courses ot' the Pennsylvania rivers. The longi- 
tudinal streams of the Jura appear to be truly consequent noon 
the folding, but the transverse streams are in most cases dis- 
tinctly not consequent, and are apparently antecedent. This 
result is of interest in itself, as a product of the most careful 
and critical study of the drainage of the Bernese Jura that I 
have yet seen. It appears to me to have an especial value in 
being reached on the ground by one familiar with the general 
natural history of rivers and their peculiar methods of develop- 
ment, as well as with the structure and deformations of moun- 
tains. Other writers have suggested explanations for the Jura 
streams, but none have so carefully examined all possible sug- 
gestions and carried their conclusions so far towards demonstra- 
tion as lias Mr. Foerste. But the bearings of his conclusion on 
my previous work have naturally a particular interest; for me. 
In their light it is necessary to withdraw the assumption that, 
the Appalachian streams were necessarily consequent upon the 
structure of the mountains when the mountains were young. 
They may have been, and valid arguments may be advanced to 
show that for the most part they probably were ; but the drain- 
age of the Jura can no longer be adduced in support of the view 
that no antecedent rivers survived the Appalachian folding. 
That the Pennsylvania drainage was originally consequent ap- 
pears to me still probable, chiefly because the deformation of 
the Appalachians was so much stronger than that of the Jura. 
It is not, however, essential to the argument that I pursued in 
the study of the Pennsylvania rivers to assume that the initial 
rivers there were of consequent location ; and it is to emphasize 
this point that I have prepared this note. The problem as it now 
appears to me stands in this position : the present courses of the 
streams have a very specialized relation to the structures that 
they flow over. This specialized relation involves a series of pe- 
culiar adjustments for its production. Then, whatever the orig- 
inal location of the rivers, it follows that whether they were 
consequent or antecedent, their present courses cannot be ex- 
plained as the persistence of their ancient original courses, but can 
find explanation only by regarding them as having changed from 
their original positions in the process of adjusting themselves to 
the structures over which they run. Hence, while the safety of 
