The example section has a variety of common rock type mixtures, which makes it a good demonstration of the interpretive power of the combined photoelectric index and neutron/density overlay. The Cherokee "Burgess Sandstone" is picked out by the density/neutron crossover which is shown to be a silica matrix effect rather than "gas effect" by the Pe value. As with the other log measures, the photoelectric index does not distinguish whether the silica mineral is quartz sand or chert. This additional distinction must be made either from drill-cuttings information or inferred from petrographic experience of correlative units.
The carbonates in the underlying Mississippian have zones with almost every mixed lithology drawn from the three endmembers of limestones, dolomites and cherts. Limestones are easily recognized as segments of Pe curve trace which are about 5 barns/electron, and a close match of the neutron and density porosity curves. At higher porosities, limestones will show minor drifts in the Pe value below 5, but these zones could equally represent either dolomitic limestone (recognized by systematically higher neutron than density porosity, but "clean" gamma-ray response), shaly limestones (higher neutron than density porosity, but indications of shale from the gamma-ray logs), or cherty limestones (density porosity higher than neutron porosity).
Cherty dolomites are sometimes difficult to discern on the neutron/density overlay alone, and may even look like limestones, because of the conflicting effects of dolomite and quartz. However, cherty dolomites are marked on the photoelectric index by distinctive shifts downward from the dolomite towards the quartz value. As with so many visual processes, the pattern recognition of lithologies from these logs is easier to do than to describe in words! After some limited practice, log sequences can be "read" for rocktype very rapidly, particularly since most zones are simple lithologies.