411 
[Foerste. 
1892.J 
the topography of the formation which once covered them. This 
theory has never been applied to the cirques of the Jura, since the 
geological conditions required for it were evidently never present : 
there is no evidence that the folds have ever been un conformably 
buried and then uncovered. 
The second theory supposes that a river held the same course 
antecedent to the folding that it does now, and that during its 
later history it was able to maintain its course in spite of folding, 
by cutting down its channel while the fold gradually rose. This 
second theory, which has been applied with success elsewhere by 
Major Powell and others, has not received sufficient considera- 
tion in an explanation of the cross valleys of the Suxe, the Birse, 
and their tributaries, as the following pages may show. 
10. Antecedent Origin of the transverse Streams of the Jura. It 
seemed at first that if the streams gradually cut across the barrier 
formed by the rising folds, then there ought to be evidences of 
this progressive action in gravels at high altitudes on the walls of 
the cirques and in erosion-benches forming broad curves on either 
side of the cirques , the lower benches successively of less curva- 
ture, and all of them representing the levels at which the river 
stood at various times, during the progress of the folding. It was 
a great disappointment not to find these direct evidences of the 
antecedent origin of the streams in the field. It seemed for a time 
as if the Boujean cirque afforded such bench marks, but the 
greater part of the fold along this cirque is composed of compara- 
tively flat-lying strata, and such benches if real prove nothing. 
Owing to the few shaly members exposed in the lower part of 
this cirque , it has developed into a narrow gorge, the picturesque 
Taubenloch, with its steep wooded cliffs, its dashing stream, huge 
boulders, and numerous pot-holes, some earlier examples of the 
latter still being obscurely indicated by depressions along the 
sides of the cliffs above. 
Although the direct evidence of the progressive erosion of the 
streams during the rising of the folds is lacking, the sys- 
tematic arrangement of several series of cirques in straight lines is 
strongly suggestive of the antecedent origin of their streams. 
This and the failure of other explanations to meet the facts are 
the main support of the theory of antecedent origin. The cirques 
of the region examined that lie in lines transverse to the folds 
are : — the Boujean and Pery, the Sornetan and Under velier, and 
