On a Quartz-porphyry from the Lake District

Extract

A Small quarry was opened about three years ago at Thwaite Head, which lies between the southern ends of Coniston Lake and Windermere. It is on the west side of the road between that hamlet and Hawkshead, and exposes a nearly vertical sill, 40 feet wide, running E.N.E.-W.S.W. in the Bannisdale slates. On the south side a series of joint-planes running parallel to the bedding of the slates and curving inwards at the top have split the igneous rock into flags, while in the body of the rock the jointing is much coarser, so that it is quarried in large blocks. Both the igneous rock and the slates are much decomposed and friable along the southern junction, and it is here a little galena is said to have been found when the quarry was first opened. This is not improbable, as the old Thwaite Head lead mine is situated not far off on the banks of Dale Park Beck.