Introduction. Geologists have long recognized the fact of the approximate parallelism of lines of dislocation in those districts in which systems of such lines are found to exist; and in my memoir on Physical Geology, published in vol. vi. part 1. of the Transactions of the Cambridge Philosophical Society, I have shown that such parallelism would, in many cases and under the most simple and probable con­ditions, be the necessary consequence of the simultaneous action of an elevating force acting beneath extensive portions of the crust of the globe. I also demon­strated that two systems of parallel dislocations might be produced by the same elevating force, the direction of the one system being perpendicular to that of the other. I also pointed out the circumstances under which, according to theory, there would be a necessary deviation from parallelism in these systems, and I indi­cated the relations which such deviations would bear, in certain general cases, to the boundary of the disturbed district, and to the particular configuration of its surface. On these points I proceeded farther, in theory, than geologists had gone in observation. There are still few districts, even in those countries with which we are geologically best acquainted, where observations have been made in suffi­cient detail to bring this subject, as a branch of descriptive geology, to the point to which I have carried it in theory.

Under these circumstances my attention was directed to the district of the Weald in Kent, Surrey and Sussex, as one in