Sortas—On the Variolite and Associated Igneous Rocks. 105 
variole as centrifugal in its growth from its earliest origin, and 
careful examination leads me to conclude that this view is correct, 
and that in this instance the central clearer space which polarizes in 
more lively tints than the rest of the variole, has been produced by 
subsequent decomposition, and develop- 
ment of silica. ‘That bubbles were pre- 
sent (fig. 7), which might have afforded 
a surface from which growth could take 
place both inwards into their cavity 
and upwards into the surrounding glass, 
is proved by the occurrence of spheri- 
cal vesicles, now occupied by chlorite 
and epidote, within the varioles. But  fy¢. 7.—A vesicle filled in with 
these have been without influence on  “blorite (Ch.) and epidote (E.). 
the variolitic growth. The occurrence of minute phenocrysts, 
originally consisting of olivine, has already been alluded to in 
describing the spilite ; it is not, therefore, surprising to find them 
within the varioles, where they usually occupy an eccentric posi- 
Fie. 8.—Variole, including minute pseudomorphs after olivine, and traversed by a 
fissure of retreat. 
tion, rarely forming the centre and serving as a nucleus. They 
now consist of chlorite, sometimes with the addition of epidote 
and calcite (fig. 8). 
