METAMORPHISM IN OIL-BEARING SHALE 755 
LITHOLOGIC CHARACTER 
The burnt shale exhibits all stages of change from slight indura- 
tion and discolorization due probably to oxidation of iron, to extreme 
hardening, and partial fusion. When slightly altered the normal 
white shale assumes a light pink color. From this stage it passes 
through various shades of rose and brick red and deepens in color to 
Fic. 2.—Hand specimen of a similar shale after metamorphism by burning 
(slightly reduced). 
a reddish, bluish, or greenish black or true black. In the advanced 
stages of change it becomes a rough, brittle, reddish, porous slag just 
like vesicular lava, like that shown in Fig. 2, or a very hard, compact, 
dark and dull-colored rock looking somewhat like a compact igneous 
rock. It is not crystalline, but the texture is variable so as to give a 
patchy appearance to surfaces. In one place it will be compact and 
black, nearby full of irregular cavities surrounded by patches of 
different colors, or again vesicular and reddish. Whereas the weight 
