in that salisbury plain coal mining district there are two (2) types of snow fences employed. one being the trench exploration for surface coal technique where the piled high chalk bank is the snow fence in the event such cursus coal trenching fails to yield any anthracite, bituminous, or sub-bituminous coal camp fossil fuels. and the other being the shaft exploration for surface coal technique where pre-planned shafts were arranged in case of failure to hold wooden snow fence panels (like the so-called ring which is two snow fence panels not a ring). they are both curved and straight like the stonehenge avenue snow fence which runs all of the way to river avon. best wishes>>8933536
this stonehenge surface coal mining district exploratory hole is the "battle of the bulge" final deep shaft and it marks the end of digging for coal, both shallow and deep, in salisbury plain's trend.
the ancients from the west abandoned their search for the preferred fossil fuel enjoyed by their ancestors further to the west, settling for the less desirable home heating fuel, smokey wood. best wishes