FIGURE 13. Chancelloria
from the Middle Cambrian Wheeler Shale, Wheeler Amphitheater, Utah (USNM
509794). A. With crossed nicols. B. Red
channel. C. Green channel. D. Image
obtained by subtracting the pixel values of C from those of B, using the Adobe
Photoshop “Difference” blending mode, adjusting the levels of the B channel
for optimal contrast, and subsequently adjusting the levels in the combined
channel. (Click on the picture to toggle between different views, or
select one of the following links: A, B,
C, D.)