FIGURE 13. Results of CaO vs. FeO analysis for volcanic glass from the "marker tuff" in the Horned Toad Formation (H4, H5) and the Lawlor Tuff from its type locality in the San Francisco Bay area (LAWLOR 1A, LAWLOR-1B, LAWLOR-2). H-5 is more hydrated and may be partially leached. Values plotted are initial values on analysis, not recalculated to 100% fluid-free basis.