GEOLOGY OF THE WESTERN ALPS. 159 



He says that elsewhere the structure of the country can 

 best be explained by the hypothesis of the Triassic age of 

 the " schistes lustres," and that we must therefore adopt 

 some other explanation of this superposition. He himself 

 describes a section at the Col d'Etache in which the 

 "schistes lustres" appear to be older than the Trias, 

 though thev there occur above it owing to an overfold. 

 Bertrand at first thought this was so conclusive that he 

 felt bound to believe that two beds of very different ages 

 had been confused together as the " schistes lustres ". But 

 on re-examination of the ground he finds that the sequence 

 of rocks there may be explained by the assumption of some 

 very complex folds. He does not offer any explanation of 

 the Mount Genevre section, but dismisses it (p. 153) with 

 the suggestion that some similar arrangement will explain 

 the superposition of the Trias on the schists. 



M. Bertrand admits that the Col d'Etache section is 

 " une serieuse difficulte " (p. 150), and that his explanation 

 is " n'est encore qu'une induction " (p. 152). He certainly 

 introduces a complex hypothesis in order to bring a com- 

 paratively simple section into harmony with his theory, and 

 this does not incline one to regard it with favour. He 

 admits that sections of Mount Genevre and the Col 

 d'Etache give no support to his view of the age of the 

 "schistes lustres"; he only maintains that they can, with 

 sufficient ingenuity, be reconciled with it. His case rests 

 mainly on his description of the northern part of the 

 country. Mount Jovet and the Grande-Sassiere are his 

 favourite illustrations. He represents these as being syn- 

 clinal mountains in which the highest bed is also the 

 newest ; for the rocks which are seen on the lower slopes 

 he thinks pass under the summit, and are continuous from 

 flank to flank. The central summit of Mount Jovet is a 

 typical "schist elustre " ; on the slopes there are Triassic 

 rocks. These M. Bertrand maintains are part of a sheet 

 which lies underneath the " schistes lustres," and are there- 

 fore older than these. In the Grande-Sassiere he declares 

 that this is shown with diagrammatic clearness. If the 

 facts are as M. Bertrand represents them, then the "schistes 



