Figure 4. Variations in the first-derivative value at 565 nm (Perkin-Elmer data set) as a proxy for hematite content in the top 5 m of selected holes. From Figure 3, it is obvious that hematite is common only in the top of these holes. From this diagram, it appears that hematite is common either at the very top of the hole or between 1 and 2 m.