and other Problems in Pyrenean Geology. 365 



slopes of the valley of Ossoue indicate infolds of Lower Devonian 

 (in a complex of other Devonian rocks), and on the ohserver's side of 

 the main valley the gentle slopes above the deep trench mark a wide 

 ontcrop of soft slates of the same age. 



It is clear, then, from this evidence alone, that there is a. prima facie 

 case that the Palaeozoics overlie the narrow outcrop of limestone, but 

 to prove that they have been overthrust further evidence on the 

 following questions is necessary. (1) Has the limestone been correctly 

 identified as Cretaceous and the rocks of the higher ground as Palaeozoic? 

 (2) Do the latter really overlie the limestone? (3) Is the junction 

 of the two a plane of movement, or can their relative positions, if 

 abnormal, be explained by a recumbent fold ? Further, the question 

 of the root of the overthrust should be considered. 



The first point is readily settled. At various places the limestone 

 yields an abundance of typical hippurites, which not only demonstrate 

 its Cretaceous age, but have enabled the French geologists to assign it 

 definitely to the Campanian subdivision. Stratigraphical evidence is 

 also forthcoming, for in Spain, in the Pinede valley, as already 

 pointed out by Stuart-Menteath,^ it is visibly continuous with the 

 Campanian of the plateau-region, where the sequence up to the highest 

 beds (Eocene) is normal. As regards the rocks of the high ground 

 between the valleys, there has never been any doubt as to their age. 

 They are sufficiently fossiliferous to show, according to all who have 

 worked on them, that they constitute a complex of Silurian, Devonian, 

 and Carboniferous rocks. By means of its fossils, that part which is 

 shown in PI. XYIII, Fig. 1, has, with the rest, been unravelled by 

 Bresson, Stuart-Menteath, and others. The unanimity with which 

 the rocks had been regarded as Palaeozoic by Pyrenean geologists led 

 to our devoting our time chiefly to other questions, especially as their 

 aspect throughout was quite in keeping with that view. In connexion, 

 however, with what follows, it may be mentioned that Bresson's 

 statement that Lower Devonian rocks form a great part of the high 

 frontier-ridge separating the cirque do Troumouse from the valley of 

 Hount-Sainte in Spain, was seen to bp justified on the occasion of our 

 traverse when Mr. Stuart-Menteath identified as Coblentzian forms 

 some trilobites, etc., which we found near the pass of la Canaou. 



Turning next to the order of superposition, it is at once obvious in 

 the field that the band of Campanian in its course along the valleys 

 generally contours the slopes in a way which is explicable only on the 

 assumption that it is the outcrop of a thin sheet of great extent but 

 slight (northerly) inclination which has been dissected by erosion, 

 but still exists beneath the Paleozoic rocks forming the high ground. 

 A closer examination confirms this conclusion, and at the same time 

 shows that the dip of the bedding in the limestone is, in general, equally 

 slight, and conforms with the junction with the basement-platform 

 of old rocks below. Steep inclinations are few and local, except near- 

 Gedre where the land disappears northward, plunging steeply, 

 according to Bresson (loc. cit., pp. 243, 249, 250, figs. 65, 69, 79), 

 beneath the Palaeozoic rocks which bound it in that direction. The 



1 "Pyrenean Geology," pt. 6 (1906), p. 26. 



