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University of California. 



| Vol. i. 



on fresh fracture, shows a very dense texture, with no visible crys- 

 tals. When it is cut with a lapidary's disk," the varioles appear as 

 round dark-gray spots, about 4 mm. in diameter, surrounded by a 

 somewhat lighter colored groundmass, and separated from the 

 latter by minutely wavy lines of demarkation, similar to those which 

 bound the varioles in Delesse's colored plate.* Numerous very 

 fine cracks traverse both groundmass and varioles. 



Under the microscope (Fig. 1 1) the varioles are seen to be com- 



Figurei 1. — Section of variolite. The lower portion shows part of a variole, 

 while above is the lighter gray groundmass, the two being 

 separated by a secondary crack. In the variole can be seen 

 the pseudocrystallites, the augite brushes, some irregular cracks, 

 and two vacuoles filled with chloritic aggregates. The ground- 

 mass shows such of the more delicate forms as are visible with 

 low power, and some crystals of iddingsite. x 21. 



posed of an open meshwork of straight, colorless rods with rather 

 indefinite boundaries, which strongly suggest at first sight the long, 

 lath-shaped plagioclases of some glassy rocks. The spaces between 

 these rods are filled with microlites in radiating brush-like aggre- 



*Sur la Variolite de la Durance, Ann. des Mines, ser. 4, t. XVII, Plate 1, 

 Fig. 3- 



