Fig. 4. Back-scattered electron scanning images: (a,b) topsoil (Ap horizon), (c,d) 25- to 35-cm subsoil (E horizon), and (e,f) 40- to 50-cm subsoil (Bt horizon). Voids occupied by resin are black, homogeneous gray areas are quartz grains, and heterogeneous gray areas are fine silt and clay particles and associated porosity (bar scale = 100 µm).