EXCURSION TO THE PYRENEES 3 I 



granitic magma, before crystallization, dissolving a portion of the 

 lime-stone, incorporating it, and thus being rendered more basic, 

 crystallizing out as a diorite about the contact. This " Roche 

 Dioritique," while as a general rule tolerably uniform in appear- 

 ance, often presents rapid variations in size of grain from fine to 

 coarse, and in other places passes into more basic forms such as 

 norite and even into varieties holding olivine. 



The excursion of the second day took the party to another 

 portion of the periphery of the same granite mass in the wild 

 district about the L'Etang de Baxouillade (see Fig. 2) and the 

 Cirque de Camp Ras. The route followed led first over the 

 granite, which as the contact was approached was seen to hold 

 a few dark inclusions, which certain of the petrographers present 

 at once set down as basic secretions from the magma. These, 

 as the little L'Etang de Baxouillade was passed become more 

 numerous and often presented the appearance of having been 

 softened and drawn out. Further on at the Cirque de Camp 

 Ras the granite comes against a mass of shale interstratified with 

 limestone. Both of these rocks are highly altered, the shales 

 being converted into dark hornstones and the limestones into 

 paler lime hornstones, consisting chiefly of a basic feldspar and 

 pyroxene. Along the immediate contact of the granite, there 

 appears to be evidence that the dark inclusions before mentioned 

 are masses of hornstone which have been separated from the 

 walls, caught up by the granite magma and more or less softened 

 — or in the case of the lime hornstone dissolved, giving rise to 

 irregular shaped masses of the "Roche Dioritique" before men- 

 tioned. One block of gneissic granite about two feet long was 

 observed, at one end of which, embedded in the granite was a 

 mass of the light-colored hornstone enclosing a mass of unaltered 

 limestone, while at the other end of the same block, the granite 

 contained small masses of " Roche Dioritique," which certainly 

 presented the appearance of dissolved fragments of the same lime- 

 stone. The only other explanation of the origin of these darker- 

 colored masses in the granite is that they are basic secretions 

 from the granite magma itself, about the margin of the mass, 



