GEOLOGY OF THE WESTERN ALPS. 161 



view helps in explaining the relations of the main gneiss 

 massifs to the structural lines in the district, which the 

 theory that these rocks are the oldest of the series leaves 

 quite unexplained. 



The whole of the first part of M. Bertrand's paper is 

 devoted to the exposition of the "fan theory," for upon it 

 he rests his belief of the Mesozoic age of the " schistes 

 lustres ". For only thus can he maintain that these schists 

 are the eastern representative of the beds which farther 

 west are not schistose. He accepts a statement which M. 

 Termier has called a "general law," that "to the east of 

 the Carboniferous band the metamorphism goes on in- 

 creasing from west to east ". So while to the west of the 

 Carboniferous the Mesozoic rocks are unaltered, to the east 

 he maintains that they soon become altered into the "schistes 

 lustres". He declares that in many places a complete 

 transition can be traced from the Carboniferous and Trias 

 to the schists ; that there is an interstratification of the 

 schists and the Triassic beds ; and that we get pockets of 

 the Carboniferous sandstone with traces of anthracite im- 

 bedded in the schists. He maintains that the " schistes 

 lustres " are therefore Triassic. He urges that for some 

 reason the beds on the eastern side of the fold were in- 

 tensely altered, so that their original characters and fossils 

 have been obliterated, and the beds turned into schists. 

 In some places this metamorphism has gone a stage further 

 and turned the beds that occurred beneath those now 

 altered into schists, into the coarse gneisses such as those 

 of the Paradiso. 



M. Bertrand's paper is not an easy one to condense or 

 to criticise. It introduces complexity in places where 

 simple explanations previously sufficed ; it flatly contra- 

 dicts the facts reported by recent workers, such as 

 Zaccagna and Bonney ; it is based on theories of mountain 

 structure now discredited ; it returns to the views of fifty 

 years ago, and ignores indispensable methods of research. 

 The theory depends on two facts: first, the gradual passage 

 Irom unaltered sediments to altered schists, especially to 

 the east of the Italian frontier; second, the interstratifica- 



