Davis.] 
418 
[April 6, 
transverse drainage was probably southward when the folding 
was begun and so continued till it was nearly completed ; but a 
broad up-arching of the middle district in relatively late time 
seems to have broken the drainage in two, and reversed the 
northern part to a northward course. 
The smaller valleys are partly cut by cataclinal consequent 
streams, and are partly etched out on the strike of the weaker 
strata by sub-consequent monoclinal or anticlinal streams. 
Supplementary Note : on the drainage of the Pennsylvania 
APPALACHIANS, BY WILLIAM M. DAVIS. 
The choice of the subject of Mr. Foerste’s essay, the Drain- 
age of the Bernese Jura, was made chiefly at my suggestion, in 
order to test the validity of a certain postulate that I had 
adopted, several years ago, in a discussion on the origin of the 
rivers and valleys of Pennsylvania. The postulate, accepted 
without special examination from the writings of several 
European authors, was briefly to the effect that the rivers of 
the Jura Mountains were essentially of consequent origin; that 
is, their courses were chosen in accordance with the form given 
to that region by the folding that it has suffered. This view 
was based upon the observation that certain transverse valleys 
cutting across the anticlinal ridges of the Jura were located as 
if they had been the outlines of lakes held in the adjacent syn- 
clinal basins or troughs, their position being determined by the 
lowest point of the surrounding anticlinal rim. An illustration 
of the evidence for this conclusion is given by La Noe and 
Margerie, which seemed convincing ; but judging by the obser- 
vations of Mr. Foerste, this illustration is not of general appli- 
cation. The postulate was employed in my discussion upon the 
rivers and valleys of Pennsylvania in order to support the pro- 
visional assumption there made as to the original course of the 
rivers in the Pennsylvania Appalachians, when those mountains 
were young. It appeared to be possible to bring about the 
present river courses from the assumed original course by a series 
of natural, spontaneous adjustments of the rivers among them- 
selves ; but the result of Mr. Foerste’s study, both on the maps, 
here in Cambridge, and on the ground, in Switzerland, has been 
completely to contradict the correctness of the accepted postu- 
