*4 REV. A. IRVING ON THE 



anticlinal flexures. Such valleys occur very frequently in the Alps 

 and elsewhere. Yon Hauer* has given us an idealized section 

 across the North-eastern Alps, representing the repeated occurrence 

 of this phenomenon among the Secondary (chiefly Triassic) strata ; 

 and I could furnish instance after instance from my own note-hook 

 in verification of his generalization. A capital instance of a line of 

 valley thus placed with reference to a great line of anticlinal fracture, 

 though quite subordinated to the main anticlinal of the whole Alpine 

 chain, has been described by me elsewhere t. All such valleys have 

 of course been widened and deepened by the erosive action of run- 

 ning water ; but it is difficult to conceive of their initiation in any 

 other way than by open fissures, since otherwise the flow of water 

 must have taken place along an elevated ridge, which is absurd. 

 Fracture, therefore, has played a part in the production of some 

 valleys ; and if so, it may have had something to do with the for- 

 mation of any lake-basins which occur in such valleys. 



3. The argument drawn from the fact (which every one will be 

 ready to admit) that lines of dislocation produced in highly meta- 

 morphosed strata must have appeared as closed lines when such 

 strata were first laid bare by denudation, does not apply universally. 

 It fails utterly when applied to the region with which we are espe- 

 cially dealing ; these valley-lakes do not occur among such strata, 

 but among well-stratified rocks of Secondary and Tertiary age. 

 Nor is it fair to reason from the close faults which occur among the 

 comparatively undisturbed strata of Secondary age in England, 

 where lakes do not occur, as to what can or cannot occur among the 

 highly disturbed and contorted strata of the Alps, where valley- 

 lakes abound. The force of this argument will be fully appreciated 

 only by those who know pretty intimately those portions of the 

 Alps to which I now refer ; seeing with one's own eyes carries more 

 conviction on this and many other points in geology than mere book- 

 knowledge can do. In some cases disturbance and dislocation of 

 strata have gone to such an extent as to invert the original order in 

 which the strata were deposited. A conspicuous instance of this 

 sort of thing occurs in North Tyrol, which was described some years 

 ago by Richthofen, and has since been more fully described by 

 Giimbeli. Between Weissenbach and Yils the strata have been 

 thrown into a sharp anticlinal, accompanied by inversion, so that 

 strata of Jurassic age are found now underneath strata of the age 

 of the lowest Trias. In the immediate proximity was once formed 

 an extensive lake, studded with numerous islets, perhaps once the 

 most beautiful lake ever produced among the Alps, though now 

 filled up by the alluvial detritus of the river Lech and its affluents. 

 On this stands the thriving modern town of Reutte. Again, in- 

 version of a similar nature has taken place about the Rigi, in close 

 proximity to the Lake of Lucerne, as Sir. A. Ramsay pointed out 

 long ago §. Hay not both these lakes be connected with fractures 



* Die Geologie, fig. 251. t Vide Geol. Mag. Not. 1882. 



\ Vide Von Hauer's ' Die Geologie,' pp. 360, 377, and fig. 254. 

 § Quart. Journ. Geol. Soc. 1862. 



