372 E. E. L. Dixon — The Gavarnie Overthrust. 



powerful lateral compression, the former play of which is sufficiently 

 evidenced by Bresson's overthrust. The intense folding to which Carez 

 refers is confined, so far as is known, to the higher horizons of the 

 Cretaceous near the frontier. His figures are beautiful views of the 

 conspicuous folds in the Danian of the upper part of the cirque of 

 Gavarnie, whereas the beds which rest on the platform are invariably 

 the underl5'ing Campanian. jS'ot only is it clear that these folds do 

 not point to relative movement between the Campanian and its ' sub- 

 stratum,' but also the only possible direction of such movement, 

 i.e. from the south, is non-suited, by the inclination of the folds, which 

 lean towards the south instead of the north, and by the fact that the 

 ' front ' of the supposed overthrust mass would be, not the folded beds 

 of the frontier as stated by Carez, but the comparatively undisturbed 

 sheet of Campanian, which extends for miles to the north. The folds, 

 as previouslj' mentioned, are readily explained as the result of the 

 southward advance of the Palaeozoic mass against resistance.] 



Thus it appears that the various facts brought forward by Carez 

 in support of his view that the Campanian rocks have been thrust from 

 the south over the basement-platform can all be explained in other 

 ways. It will have been noticed that he adduces no direct evidence 

 of movement along the supposed thrust-plane, though he remarks 

 (p. 1155) that the surface of the basement-platform is " rabotee, je 

 dirai meme polie." Very likely this surface in places is a plane of 

 movement, seeing that it separates rocks of very different rigidities 

 and occurs but a short distance below the great overthrust previously 

 described, but, as we shall now see, there is every reason to believe 

 that it is generally a surface of original deposition. 



It may be readily examined near Gavarnie in the valley-side to the 

 south-west of the bridge at La Prade de 8aint-Jean, where the base- 

 ment-platform appears to have been forced by intense lateral pressure 

 to take in one of the sharp ' tucks ' previously mentioned (p. 366), 

 in which has been nipped a crushed syncline of the overlying 

 Campanian limestone, in the form of a long tongue passing down 

 obliquely for a considerable distance into the mass of crystalline 

 schists. This tongue, which had been previously discovered by 

 Mr. Stuart-Menteath, we found to be bounded along its southern 

 wall by a shear-zone which had affected schists and limestone alike, 

 but at the bottom it was evident that the junction left the plane of 

 shearing, and along the other wall showed its character that it was 

 a surface of deposition unmodified by shearing or friction-brecciation. 

 The limestone adhered closely to the schists, filling inequalities in 

 their surface, and showed no trace of subsequent miJvement, either 

 in its matrix, which was similar to and continuous with the rest of the 

 Campanian, or in the included fragments of hippurites, which would 

 have at once betrayed shearing by their distortion, even though the 

 intermingled quartz-fragments retained their original form. Also 

 the latter were certainly more numerous than at higher horizons of 

 the Campanian, where, Carez says (p. 1154), they also occur 

 " dissemines dans toute la hauteur de la couche." 



Although it is sufficient, in order to disprove Carez' overthrust, to 

 show at any place that the junction of the Cretaceous limestone with 



