1892.] 
401 
[Foerste. 
enlargement and shaping, they are certainly not simple valleys of 
erosion. It is evident that the streams could not have broken 
through the massive ramparts formed by our chains [mountain 
folds] if they had not found a crack, a dislocation more or less 
, complete, which would permit them to flow across these ramparts 
[folds].” Jaccard, however, appreciated the effects produced by 
erosion proceeding from streams now occupying the valleys, more 
than previous writers on the Jura had done. L. Rtitimeyer, 
although a very advanced thinker in this line of studies, and 
unusually happy in his observations, still believed that the Jura 
cirques were cracks. “ Usually linear dislocations are more apt to 
form longitudinal valleys rather than cross valleys. Atmospheric 
precipitation in such dislocated countries is therefore more apt to 
And longitudinal courses of transportation than cross-drainage- 
courses, and the former must to this extent be considered theoreti- 
cally older than the latter. However, on elevation of the land 
[folding?], inclined surfaces will be formed, which at once pro- 
duce drainage in the direction of steepest slopes ; and, at least 
at the fault planes along inclined strata, the mechanical action of 
water will for many reasons be far greater than in already existing 
longitudinal drainage courses. The growth of cross valleys will 
therefore in such circumstances anticipate the deepening of longi- 
tudinal valleys, and cross valleys will therefore be more apt to suc- 
ceed in serving as drainage channels for longitudinal valleys than 
the reverse.” Rutimeyer therefore believed that, especially along 
cracks, side streams would cut valleys out across folds, and then 
having gained an exit themselves, also serve as means of exit to 
more or less of the main stream occupying the synclinal valley. 
J. B. Greppin held substantially the same views as Jaccard. A. 
Heim denied most emphatically that cross valleys are due to cracks 
left by faulting. Tunnels under the beds of cross valleys have 
failed to show such faults. Above ground the strata on either 
side of the cross valleys show perfect agreement. The origin of 
cross valleys he therefore ascribed to denudation and erosion, the 
streams cutting their way backwards into the folds. If two such 
streams cutting their valleys back into the fold should meet, then 
they would cut through the fold. If the rate of slope on the two 
sides be dissimilar one valley secures the prestige and turns the 
stream of the other valley aside into its own channel. O. Peschel 
again denies the origin of cirques from the erosive action of streams. 
PROCEEDINGS B. S. N. H. 
VOL. XXV. 
26 
AUG. 1892. 
