250 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 13, 



But this explanation is totally inapplicable to the Appalachians. It 

 is almost impossible also to apply this reasoning to the Alps, from the 

 absence of masses of erupted matter adequate to account for the phae- 

 nomenon by displacement. But, however we may theorize, it must 

 be admitted, that in nearly all the alpine folds to which my attention 

 was directed, the longer leg of each anticlinal slopes towards the centre 

 of the chain, whilst the steeper talus or shorter leg of the flexure is 

 away from it (see figs. 12 & 14, and Plate VII.). Besides the occur- 

 rence of this phsenomenon, which is the basis of the theory of Professor 

 Rogers, the Alps seem further to exhibit, as far as I know them, 

 the same longitudinal faults as the Appalachians, whereby fractures 

 ha\dng occurred either on the most bent portion, or the steep side of 

 the anticlinal or synclinal folds, the result has been (explain it how 

 we may) the lateral overlapping of the older rocks upon the younger. 

 In saying that I am not prepared to subscribe to the earthquake 

 theory, I have to thank Professor H. Rogers for having drawn dia- 

 grams to explain two of the most frequent cases of such overlap and 

 inversion, as they occur indeed in my own sections, showing how the 

 axes of each trough or ridge were first forced into oblique positions, 

 followed by the fractures in question, and then by the transgressive 

 sliding of older over newer deposits by lateral pressure. The fol- 

 lowing is his explanation. 



" I have endeavoured (says Professor Rogers) in the annexed 

 diagrams to illustrate two very common kinds of faults or dislocations 

 occurring in regions of closely-compressed or inverted flexures. In 

 one case (fig. 29. Nos. 1, 2 & 3) the fracture coincides, or very 

 nearly so, with the anticlinal axis plane and the plane which cuts the 

 two branches of the anticlinal flexure at the same angle ; the other 

 instance (fig. 30. Nos. 1, 2, 3) is where the dislocation is in the syn- 

 clinal axis plane. The displacements here shown are both of them 

 upcasts along the inclined plane of the fault. In all oblique com- 

 pressed flexures, this plane of the fault dips of necessity towards a 

 more disturbed side of the district. The eifect of both of these 

 classes of fracture is to bring an older set of strata superimposed in 

 approximate parallelism of dip upon a newer series, but with oppo- 

 site conditions, the anticlinal fracture inverting the beds on the side 

 below or beyond the fault, while the synclinal fracture inverts those 

 on the upper or nearer side : I think it will be found that the first 

 phasis is by far the most common in the Alps. The greater part of 

 the dislocations of the Appalachian chain are certainly of this cha- 

 racter, the fracture being either in the anticlinal plane or a little be- 

 yond the axis, in the short inverted leg of the flexure. Most of the 

 cases of inversion in the Alps which your interesting sections display, 

 and to which you have kindly drawn my attention, are, I think, 

 simply instances of dislocation along the anticlinal planes of inverted 

 or closely -compressed oblique flexures. A few, however, appear to 

 have resulted from faults along the synclinal planes. I have not 

 here exhibited the other less usual forms of dislocation, or treated of 

 the cases where the displacements are downthrows and not upthrows 

 along the inclined plane of the fault." 



