4 O FRA NK DA WSON A DA MS 



during their recrystallization to marble have had added to 

 them, in certain cases at least, as Lacroix holds, a certain 

 amount of new material, probably from the waters and exhala- 

 tions accompanying the intrusion ; but this infusion of new 

 material seems to be confined to a narrow zone about the con- 

 tact, and is not by any means a regional phenomenon. In fact, 

 in the occurrences at the Cirque d'Arbisson, some of the lime- 

 stones of the Cirque itself, while greatly contorted, are practi- 

 cally unaltered in character, still retaining their original blue 

 color and fine texture, and are free from all foreign minerals. 

 The occurrence of axinite about the contacts does not seem to 

 call for any especial notice, seeing that boron exhalations, giving 

 rise to tourmaline, have been recognized as of frequent occur- 

 rence in contact zones by all authorities, having been found by 

 Rosenbusch, even in the Barr-Andlau contact zone, which is 

 always cited as affording evidence of the strongest kind, of the 

 absence of metasomatic changes in the rocks about granite 

 intrusions. 



As mentioned above, in the district visited on the first two 

 days of the excursion, that is, in the district about Lac l'Estagnet 

 and the Cirque Camp Ras, there is between the altered lime- 

 stone and the granite a zone, varying greatly in width but usually 

 quite narrow, of what Lacroix terms " Roche Dioritique," and 

 which is considered by him to have been formed by the solution 

 of a portion of the limestone in the granite magma. This rock 

 is said by Lacroix to occur only where the intrusion has lime- 

 stone as a wall rock. It is a rock generally grayish in color 

 and more basic in appearance than the granite, but of about the 

 same size of grain, varying, however, considerably in grain and 

 character from place to place. Lacroix states that a detailed 

 study of it shows that it is not uniform in composition, but that 

 it varies in minerological composition from a hornblende granite 

 to a basic olivine norite, or even a peridotite. It completely sur- 

 rounds detached masses of limestone, and has distinctly the 

 appearance in the field of having been produced, as Lacroix 

 believes, by a solution of the limestone along the margin of 



