Figure 7. (A) Photograph of slabbed drill core shows brittle, reddish-brown, layered soilstone crust that occurs as an unconformable unit on top of the Miami Limestone oolite. The crust also caps the Key Largo Limestone coral reef. The core shown was taken in the Saddlebunch Keys (SB) in the lower Florida Keys (Fig. 6C). (B) Terminology used to describe geologic time in this report. A period of nondeposition, weathering, or erosion creates an unconformity, a surface that separates a much younger overlying rock or sediment layer from the underlying rock or sediment layer. In the core sample (A), a prolonged period of lowered sea level caused nondeposition. Note area where the top of the oolite was dissolved by fresh water (rain) and became mixed with the soilstone crust (also called calcrete). Sea level has not been as high as it was at ~125 ka (125,000 years ago) when the Key Largo and Miami Limestones of the Florida Keys accumulated.