"Mark Godden's Little Bit Of Cyberspace Mk.II"

The Orientation of Major Joints within the "Freestone series" on Portland

The diagrams below show most of the major joints, used by Portland's quarrymen. There is a little local variation (approximately plus or minus 5 degrees) and the bearings given are an average of several readings taken for each joint type in each area. The consistency between different areas of Portland is fairly good and it can be seen that in each diagram, looking from "the west" (or the left), the angle subtended by the Souther and East n' wester is greater than 90 degrees which is why traditionally quarrying on Portland generally always proceeds "from left to right" as stone is more easily removed.

The annotated photograph below, attempts to illustrate the relationship between coastal erosion (and hence the geomorphology of Portland Bill) and the weaknesses caused by the jointing system in the area. The joint directions for Portland Bill (given above) have been superimposed onto the photograph where the direction of coastline shows a definite correlation to the jointing pattern, this relationship is apparent for just about the whole of the island's coastline.

The well known diagram reproduced below was produced by Mr S.S.B Hounsell, Quarry Manager and Director of the South Western Stone Co Ltd. (originally published as part of their publicity material in the 1950's). It shows the typical (idealized) jointing pattern that can be found right across the Island.

Note: Rangers and North-easters are minor joints, not present at all locations.