SPRINGS AND THOSE OBSERVED IN AMYGDALOIDS ETC. 85 



EXPLANATION OF PLATE IV. 



Fig. 1. Opal with hyalite in globules forming numerous veinlets in brick. 



Enlarged 180 diameters. (White parts, opal; light dotted parts, 



hyalite ; dark parts, brick.) 

 Fig. 2. The central portion of the principal vein in fig. 1. Enlarged 600 



diameters. 

 Fig. 3. Ohabasite and crystallized mesotype in a geode of the brick. (The 



magnesian mica of the brick is shown by the dark streaks. 0, chaba- 



site ; M, mesotype.) 



