The Imperial College borehole test site is situated in the the county of Northumberland, England. It consists of four vertical 250 metre boreholes positioned as in figure 1. The holes intersect an Upper Carboniferous cyclical sequence of sandstones, shales and limestones. (see Figure 2a) Holes 1 and 2 have been fully cored and all holes have been extensively logged. Although the bedding is approximately horizont al over the area of the site, minor faulting has been identified. This is very clearly indicated in the FMS data which has been acquired in all four holes.