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Phanerozoic-Clast
Breccia: Breccia clasts in a shale matrix that was originally
stripped from the land surface, mixed with ejecta in a ground
surge and quickly transported back into the crater by seawater.
Found above all crater regions.
Ejecta: An overturned sequence of clastic sedimentary
rocks thrown from the crater during formation. Found only on the
terrace terrane.
Keweenawan
Shale Clast Breccia: Broken and partially melted billion-year-old
black shale and melt-rock grains. Found only on the central peak.
Crystalline-Clast
Breccia with a Melt-Rock Matrix: Similar to crystalline-clast
breccia with a sandy matrix, except the sandy matrix has been
melted and is dominated by powdered crystalline rocks and impact
melt-rocks. Found only on the central peak.
Crystalline-Clast
Breccia with a Sandy Matrix: Smaller blocks of granite
and gneiss in a matrix of silt to sand-size rock fragments. Found
only on the central peak.
Proterozoic Basement Blocks: Large blocks of granite
and gneiss which form the core of the central peak and extend
below much of the crater floor. Found only on the central peak.
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