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.)