EXCURSION TO THE PYRENEES 45 



zones. What is required to establish this, is an exhaustive series 

 of chemical analyses of carefully selected material, showing the 

 composition of certain definite beds in their original and altered 

 forms. Such an investigation would be of the greatest interest 

 and highest importance to geological science at the present time. 



Although, therefore, it is possible that some of the Archean 

 gneisses which now have no longer the composition of any 

 ordinary sediment, may represent shales which have been trans- 

 fused with new material by emanations accompanying granitic 

 intrusions, the studies hitherto made of these Pyreneean con- 

 tacts do not, in the opinion of the writer, afford any conclusive 

 evidence that such emanations have this transforming power. 

 Still further are they from establishing the contention that 

 granitic intrusions are merely great areas of shale or other sedi- 

 mentary rocks changed in situ into granite, which is the view of 

 their origin held by Michel-Levy and Lacroix. "Je considere 

 done toutes ces couches metamorphiques isolees aujourd'hui au 

 millieu du granite comme le residue non digere des assises sedi- 

 mentaires dont le granite a pris la place." 1 "La mise en place 

 du granite s'est effectuee par dissolution graduelle des roches 

 sedimentaires dont il occupe la place." 2 This conclusion would, 

 of course, if established, be of the greatest interest, but the 

 evidence hitherto put forward seems quite insufficient for that 

 purpose. 



The metamorphism of the sedimentary strata in the vicinity 

 of the intrusions of the basic rocks (ophite and lherzolite) is 

 also attributed by Lacroix largely to the action of emanations 

 from deep-seated sources. " L'impuissance de la lherzolite a 

 operer des transformations metamorphiques par Taction de sa 

 propre substance est demontree par l'absence de zones de pas- 

 sage entre elle et les sediments metamorphiques et par la nature 



des mineraux produits a son contact La roche modifiee 



a fourni une partie des elements necessaires a la formation des 

 mineraux neogenes, mais beaucoup de ces elements ont ete 



'Lacroix: Livret, Guide, p. 15. 



- Lacroix, Le granit des Pyrenees, etc., p. 3. 



