EXCURSION TO THE PYRENEES 39 



more or less incomplete study of the several occurrences. The 

 members of the excursion were, moreover, at a serious disadvan- 

 tage in not having any geological map of the districts visited. 

 It was never possible to ascertain, except in a most general 

 way, the areal distribution of any rock, the extent of any 

 intrusion, or the distance to which any metamorphic changes 

 could be traced. In preparing these notes, however, the infor- 

 mation obtained in the field has been extended by a careful 

 study of Professor Lacroix's published works, so far as they 

 bear upon the localities in question, and a considerable number 

 of thin sections of the rocks collected from the various occur- 

 rences, have also been examined. 



In those cases where the granites of the Pyrenees were seen 

 in contact with limestones, as, for instance, in the occurrences 

 about Lac L'Estagnet, Pic du Camp Ras and Cirque d'Arbisson, 

 the limestones near the contact were observed to contain various 

 silicates which had crystallized out in them, as described above. 

 Lacroix considers that in these cases, original differences in the 

 composition of the beds influenced the nature of the minerals 

 developed by metamorphism, but that the material for their 

 growth was largely supplied by emanation from the intrusion. 

 He believes that in the case of bands which were originally pure 

 limestones, the minerals produced are garnet, epidote, zoisite, 

 pyroxenes, amphiboles, quartz, feldspars and axinite. Where 

 the original beds were impure, through the presence of siliceous 

 or argillaceous materials, they are transformed into epidosites, 

 garnet rocks, or feldspathic hornstones. Such limestones with 

 silicates scattered through them, are not, of course, peculiar 

 to the Pyrenees, they are seen in every Archean district in the 

 world where limestones are found. The question always pre- 

 sents itself, as to how far these silicates represent original 

 impurities in the limestone, and how far they are due to exhala- 

 tions accompanying igneous intrusions. The limestones abutting 

 directly against the igneous mass, even in the Pyrenees occur- 

 rences, are often free from these silicates In these contacts, 

 however, the appearances go to show that the limestones 



