Figure 2. A, Quartz-alkali feldspar-plagioclase feldspar diagram (modified from Streckeisen, 1976) showing modal compositions of Middle Proterozoic rocks shown in
table 1. Modes counted on Na-cobaltinitrate-stained rock slabs and thin sections.
B, Normative feldspar plot (O'Connor, 1965) of Middle Proterozoic rocks in the Harpers Ferry quadrangle (numbers refer to samples in
table 1).
