Fig. 17. Harker diagram showing trend of data for MgO wt. % versus SiO₂ wt. % in the Ore Bed Road, Fowler, and Fullerville granites and related Popple Hill gneisses. Data are from Carl (1988), Carl and deLorraine (1997), and Table 1. Solid diamond = Popple Hill gneiss (98 and 99) coexisting with Fowler granite (98A, solid square) and paired Popple Hill biotite gneiss (114, solid diamond) and Fowler granite (113; solid square); open square = Fowler granite from Carl and deLorraine (1997); solid triangle = Fullerville fine-grained granite (118) and megacrystal granite (123) in association with Popple Hill gneiss (121, solid diamond); open triangle = Fullerville granite and open circle = Ore Bed Road granite from Carl and deLorraine (1997); other solid diamonds = least altered Popple Hill gneiss (Engel and Engel, 1958); and open diamond (M) = average of 7 Popple Hill mesosome gneiss samples (+/- 1.81 wt. % SiO₂; +/- 0.74 wt. % MgO) and open diamond (L) = average of 4 Popple Hill leucosome gneiss samples (+/- 4.03 wt. % SiO₂; =/- 0.16 wt. % MgO).