I Will now put forward some details, for it seems necessary that some proofs of what has been maintained in general should be given, and I shall therefore quote some examples of the intimate connexion between earth-structure and terrestrial magnetism. No diagrams could indicate the relations better than Locke's Magnetic Sections across the Hudson, which were taken at three different points of the Palisades, Snake Hill, Fort Lee and Patterson (see Plate XV.). The dip and intensity were in each case determined at a number of points along a line perpendicular to the range of cliffs, and the curves rise very suddenly to maxima just above the edges of the cliffs, which are composed of columnar diorite. This diorite is widely distributed and lies between masses of Triassic sandstone; the dip is slight and towards the west.