Can't view the image, but I've looked at old maps online 1871-4 when it was all farmland and the pond or whatever seems to be on quite a sloping area, steeper-banked on the western/uphill side, in what is now the gardens of Croome Drive backing on to Burlingham. Don't know about further downhill, but up on Croome Drive the soil is very sandy and shallow, no sign of clay. In my daughter's garden in some places there's only about 6" of soil before you hit bedrock.