The area considered in this study is roughly the drainage of the Wharfe and its tributary the Skirfare, above Burnsall, a typical ‘Yorkshire Dale’. The valley is excavated through the Yoredale series of alternating limestones, shales, and sandstones, into the Great Scar Limestone, the lowest member of the Carboniferous series. This lower limestone forms very imposing and massive scars along the valley sides, above which the fells rise in a series of steps and scars corresponding with the limestone and sandstone outcrops. The valley bottom is occupied by a series of glacial lake flats and moraines which have played a very important part in the settlement of the valley, the lake flats being swamp until recently drained, and still liable to flood through a great part of winter, the moraines providing dry crossing places and village sites throughout the upper dale. The dale under discussion is about 20 miles long, and from ¼ to ½ mile wide between the lower scars of limestone. The valley floor rises from 500 ft. above sea-level at Burnsall to 1250 ft. at the head of the valley near Oughtershaw,while the top of the first scar varies from 800 ft. to about 1600 ft., being a platform of good pasture about a third of a mile wide, on each side of the valley.