1892.J 
395 
[Foerstc. 
has not been so marked. Although the softer, more recent strata 
have been pretty generally removed from the crests and the 
flanks of the folds, a sufficient mass remains to preserve to a 
marked degree the topography produced by the folding. A 
young drainage, consequent on the folding, might be expected 
here if anywhere ; indeed, when the study of the Jura drainage 
was first undertaken, there seemed to be no evidence of the 
remains of antecedent drainage, or of the existence of river 
courses due to faulting. Further study has, however, led to dif- 
ferent conclusions, as will be seen in the following pages ; but as 
far as known the Jura still offer the most typical cases of initinl 
drainage consequent upon folding. 
This paper is limited to a study of the drainage of the Suxe and 
and Birse rivers, comprising the major part of the drainage of the 
Bernese Jura. The “Description Geologique du Jura Bernois” 
for the Swiss Geological Survey, by J. Greppin, is the latest ex- 
tensive geological study of the area (1870), and has been utilized 
as basis for the geological views here expressed. The topography 
has been taken chiefly from the excellent contoured maps, on the 
scale of 1 : 25,000, published by the Swiss government. 
GEOLOGY OF THE BERNESE JURA. 
2. Deposition and Sequence of Strata. — The lowest strata 
exposed in the Bernese Jura are of Triassic and Liassic age, and 
wherever erosion in this area has been sufficient these strata have 
been exposed, so that their continuous extension seems probable. 
From the beginning of the Lias the entire region continued to 
be an area of deposition, until the beginning of the Pterocerian 
epoch, the middle of the upper Jurassic division. At this time a 
gradual elevation of the land took place. The elevation was 
more pronounced in the northeastern part of the Bernese Jura, 
so that this portion first rose above the sea. As elevation con- 
tinued the sea retreated towards the southwest. Thus, during 
the Pterocerian epoch, sea deposits did not extend northeast of a 
line connecting Lauffen, Schelten, and Balsthal, and the north- 
eastern corner of the Bernese Jura area was dry land. During 
the Virgulian epoch, sea formations did not extend north- 
east of a line connecting Charmoille, Undervelier, Grandval, and 
Solothurn, one third of the Bernese Jura district rising above the 
sea. During the Portlandian, no marine deposits were formed 
