Unbroken siltstone with occasional interbedded shale occurs between 34 and 45 m. Below 45 m are various shales, clays, and coal beds. The lithology is illustrated in Figure 2 by the strip log for IH1. Fragments from the brecciated zones commonly have red exteriors and yellow interiors, indicating that they were broken before they were oxidized. The extent of the fracturing may be due to the relieving of the stresses set up by the burning coals.
Later oxidation is due to atmospheric and groundwater circulation through the open fracture system.
It is apparent that the uppermost 34-m of section bears little resemblance to an ideal homogeneous isotropic medium. It would seem plausible that the seismic observations in the clinker area might be explained in terms of wave phenomena in a heterogeneous medium. A similar wave-test section was prepared from signals recorded in the mesa along Line 0001. The spread extended from 240-ft. Various possible causes of reflection quality deterioration on the clinker were considered before the field tests were designed.