In those parts of Britain upon which all geologists are agreed with respect to the natural order of their ascending series of rock-formations, the stratigraphy is of a comparatively simple character. The beds are either gently inclined, or but slightly convoluted. The rules by which the original sequence of the strata is worked out have been settled by common consent. The nature and effects of those physical accidents which have affected the rocks subsequent to their deposition have long since been almost exhaustively worked out. The rules and conclusions thus developed are now-a-days part and parcel of the working material of every field-geologist worthy of the name.