When rock strata vary laterally in thickness, composition,
or other features, geologists construct a cross-section to document this variation.
Cross-sections may be recorded as a simple sketch, a mosaic of overlapping photos,
or a series of measured sections along the face of a quarry or other outcrop.
Cross-sections are particularly important in studies in ancient reefs. This example
from Lime Kiln Park, constructed by tape measurements along the quarry face, shows
the relation between reef and interreef deposits.