Sorzas—On the Variolite and Associated Igneous Rocks. 99 
lines, which appear to proceed from the side of a felspar lath, 
diverging from it at angles of about 60°. It thus suggests the 
reedy form of augite with feathered edges seen in some glassy 
rocks, but no connexion with augite can now be traced, if any ever 
existed. The felspar laths are often bent, partly as a consequence 
of earth pressure, by which they have also frequently been broken 
across, partly by trichitic growth. Angles of extinction have been 
measured exceeding 20°; the species is therefore probably andesine. 
Augite appears to have been originally present in small grains, 
situated in the interstices left between the felspar; it is now 
entirely converted into pale-green chlorite. Hpidote is thickly 
scattered in small crystals through the rock, and calcite, which has 
replaced much of the felspar, is similarly dispersed. Calcite also 
fills up the cavities of the vesicles, which, though sometimes more 
or less oval in outline, are more frequently of quite irregular shape, 
bridged across by threads of rock, or invaded by promontories. 
Felspar laths sometimes project into them, forming with their 
surrounding film of altered glass tent-like eminences. The 
infilling calcite occurs as a mosaic; its cleavage planes are some- 
times curved or otherwise distorted; in some cases it presents a 
fan-shaped radiate structure, but this does not appear to be 
original, for distorted cleavage planes of earlier calcite grains can 
be traced across the rays of the fans, which would thus appear to 
result from the action of pressure on a once existing mosaic: fur- 
ther illustration of the action of pressure is afforded by lines of 
typical cataclastic granulation, which cross some of the calcite 
mosaics, in precisely the same fashion as the familiar crush lines in 
quartz mosaics of granite. 
From this rock, with its intersertal structure and slight traces 
of original glass, up to the completely variolitic modifications, 
there is every stage of transition, affording a complete passage 
from the variolites “du Drac” to those ‘‘de la Durance.” The 
prevalent rock of the area does not differ in general character from 
the foregoing, but a greater tendency is observable on the part of 
the felspar'to long curvilinear growths in sheafy aggregates, and 
in some cases this becomes so clearly expressed that the structure 
of the rock might properly be described as diffusely spherulitic. 
The examples in which this is best displayed are very much broken 
rocks, cracks now filled with calcite traverse them in all directions, 
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