and other Problems in Pyrenean Geology. 369 



Port-Bieil and other places along the southern margin of the overthrust 

 Palaeozoics. 



9. Intensely folded nature of the Upper Cretaceous. 



The following is a summary of his expansion of these arguments, 

 with comments in square brackets : — 



1. He has "not seen a single pebble at the base." In places the 

 lowest beds contain quartz grains or some subangular fragments of 

 quartz, but the latter are very rare and disseminated also throughout 

 the limestone. The subangular fragments of the ' substratum,' which 

 are found, though also very rarely, at the base, are more easily 

 explained on the hypothesis of an overthrust than on that of a trans- 

 gression of the Cretaceous sea. [It appeared to us, on the contrary, 

 that quartz-fragments were frequent at the base of the limestone, 

 but rare or absent at higher horizons. Their evidence, however, is 

 inconclusive, though the hypothesis of an overthrust leaves un- 

 explained the general absence of fragments of other hard rocks, which 

 make up a large part of the ' substratum.'] 



As regards the basal fauna, Carez doubts whether it is littoral, as that 

 of the Lower Danian is deep-sea, but in any case it merely indicates 

 a slight depth of water, not the proximity of a coastline. [Here 

 again the evidence is inconclusive, though the persistence, apparently 

 admitted by Carez, over a wide area of an exceptional fauna in the 

 'sole' of the supposed overthrust is remarkable.] 



2. Carez says that the surface of the 'substratum' is "planed 

 down, I will even say polished." He further remarks, as opposed to 

 Bresson's idea that this surface is a sea-bottom, that "the erosive 

 action of the sea is exercised on its coasts, but never on the bottom." 

 On the other hand, the smoothing of the ' substratum ' of an overthrust 

 is to be expected, and ' ' the presence of a plane surface beneath the 

 Cretaceous, so far from proving the latter's deposition in place, is one 

 of the best arguments in favour of the theory of cliarriage.^'' [This 

 argument would, in fact, be almost conclusive, were the surface of the 

 ' substratum ' everywhere polished. But though this may be the case 

 in places, it certainly is not universally so, and the occurrence of even 

 a single place yielding clear evidence that the limestone has been 

 deposited on the ' substratum,' such as that described later (pp. 372-3), 

 is sufficient to disprove Carez' cliarriage. Instances of movement and 

 polishing along the junction are to be expected in view of the great 

 overthrust, previously described, a short distance above. IS'evertheless, 

 at the cirque de Troumouse (p. 366), where mylonisation was noticed 

 at the base of the limestone, the evidence pointed, not to a general 

 movement along the junction, but to a local one crossing it.] 



3. Carez remarks that the Upper Cretaceous of Gavarnie and 

 neighbouring places belongs to the southern or hippurite-limestone 

 facies, whereas contemporaneous beds to the north, though at one 

 place distant merely a mile, yield a northern fauna which is com- 

 pletely difierent, an abruptness of change which cannot be original. 

 [Other disturbances, known to exist in the neighbourhood, may account 

 for this abruptness of change. Of the minimum distance necessary to 

 have effected the change in the Cretaceous sea our knowledge is probably 

 uncertain.] 



DECADE V. — VOL. V. — NO. VIII. 24 



