THE EXCURSION TO THE PYRENEES IN CONNEC- 

 TION WITH THE EIGHTH INTERNATIONAL 

 GEOLOGICAL CONGRESS 



The origin of the ancient crystalline rocks of the earth's 

 crust is a subject which has always possessed a peculiar interest 

 for geologists and which, now that the progress of investigation 

 seems to bring the solution of the various problems connected 

 with these rocks almost within our reach, has a greater attraction 

 than ever. 



One of the most important lines of evidence bearing upon 

 this question is that derived from the study of the contact zones 

 about intrusive masses, but the effects produced by many of these 

 intrusions have been differently interpreted by different observers. 1 

 In France especially, Michel-Levy, Barrois and Lacroix have 

 described intrusive granite masses, which have not only intensely 

 altered the strata through which they pierce but which have pro- 

 duced a wholesale transformation of the sedimentary rocks in 

 question into granite, the granite now occupying the space 

 formerly occupied by the sediments. If this be the origin of 

 granite, a knowledge of the fact would have an important bear- 

 ing on the interpretation of many occurrences in the Archean, 

 but the great majority of geologists have been unable to find 

 evidence of it in their respective countries. The French Pyrenees 

 have, however, been cited by Lacroix as a district in which these 

 remarkable transformations could be seen with especial clearness, 

 a"d in connection with the International Congress of Geologists 

 held last summer in Paris, an excursion to the Pyrenees was accord- 

 ingly arranged, under the leadership of Professor Lacroix, in order 

 that the members of the congress might have an opportunity of 

 seeing these transformations in the district made classic by Pro- 

 fessor Lacroix's work. It is proposed in the present paper, first 



1 Adams, F. D.: A review of some recent papers on the Influence of Granite 

 Intrusions upon the Development of Crystalline Schists. Jour. Geol., Vol. V, 1897. 



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