524 Corres2)on(/eiice — P. W. Stuart- Menteath. 



defined as beneath the Silurian and although its types were selected 

 from the heart of the Cretaceous. As at the valley of Ossoue, so at 

 every point where limestone occurs in the Archaean basis of Mr. Dixon, 

 there is a visible synclinal descent of the Cretaceous into the said 

 basis. At Eaux Chaudes the same Hippurite limestone descends 

 into the granite basis at the valley of Bitet, and is similarly penetrated 

 by microgranulite ; being especially metamoi-phosed at contact with 

 intrusions of Porphyry, termed Andesite and Labradorite on the map, 

 which porphyry traverses the main granitic mass, and is itself traversed 

 by a white gi'anulite common at Gavarnie beside the synclines of 

 Cretaceous. To Mr, Dixon's classification of the Gavarnie basis as 

 Archsean I have no objection, provided that, with many geologists, 

 I may interpret such Archaean as an imperfectly cooked example of 

 a magma that is frankly eruptive at other points. Certainly around 

 Gavarnie this magma was so plastic as to permit the descent of thin 

 sheets of Cretaceous to three hundred yards in depth, and to exhibit, 

 at visible points of contact, the most distinctive features of irruptive 

 intrusion. Around Eaux Chaudes vast portions of the Hippurite 

 limestone are converted into white crj'stalline marble, irregularly 

 mixed with ferruginous and dolomitic segregations. Their irregularity 

 forbids their attribution to those dynamic influences which Sauer 

 and others have controverted in the Alps of Glarus, where augen 

 gneiss is as irruptive as at Gavarnie. Finally, at the Ossoue valley 

 and elsewhere around Gavarnie, I have traced the constant presence 

 of the ' Permian ' of Pinede, passing insensibly into a peculiar gneiss 

 crammed with ferruginous concretions. M. Bresson admits its 

 presence in his latest papers. In the Pinede valley it is eaten into 

 by the homogeneous granite, and reduced in places to a conglomerate 

 of granitic basis. 



One other point may be recommended, without offence, to future 

 observers. South of Gavarnie the Spanish plateau is composed, 

 for many miles, of that Flysch which I introduced and defined in 

 1881 as that of the Vienna basin. Over a thickness exceeding 

 2,000 feet it exhibits the Helminthoids, composition, and very 

 peculiar structure of that formation. Between Torla and Paulo it 

 overlies the Danien as regularly as throughout the Spanish Pyrenees. 

 The denial of the possibility of its post-Danien age, and the denial 

 of its association with gypsum and salt, form the basis of the 200 

 pages of the latest French Survey Bulletin by M. Leon Bertrand. 

 Yet in Spain, as in France, it presents characteristic Nummulites, 

 which are ignored as deliberately as my Hippurites of Eaux Chaudes 

 in 1885. In three papers of the Biarritz Association I have invited 

 verification of the facts. The peculiarity of this formation is its 

 alternation of tranquil and violently contorted portions, and its 

 abundant evidence of local volcanic action. Some of these have been 

 recently verified by Professor Fournier. But the formula " a priori 

 inexact" has been more popular than observation, and is confirmed 

 in Mr. Dixon's conviction that my references to current Palaeontology 

 have no connection with matters wholly decided thereby. On 

 Mr. Dixon's own map the extent of the supposed ' thrust-plane ' 

 can be measured as 8 kilometres, yet he adds 2 kilometres in 



