582 JAMES ASTON 
COMPARATIVE MICROGRAPHS 
Figures 9, to, and 11 show the striking similarity between the 
structure of rocks and alloys as revealed by the microscope. In each 
case the rock-section is on the right, beside its analogous alloy-struc- 
ture on the left. 
In the upper left-hand corner of Fig. 9 is the structure of a three- 
component mixture of 74 per cent. Bi, 55 per cent. Sn, and 21 per cent. 
Fic. 9 
Pb. The excess bismuth has separated out into the white masses; sur- 
rounding these is the binary eutectic of bismuth and tin, and finally, 
as the central black constituent, we note the ternary eutectic. A 
somewhat similar rock-texture is on the right, a rhyolite with the 
white quartz, the dark orthoclase, and the finer remaining ground 
mass. 
Below on the right is a section of Augite porphyry, with the white 
plagioclase, adjoining this the gray augite, and inclosing all the fine 
texture of the ground mass of plagioclase and augite. It is very simi- 
