Two years ago Mr F. L. Ransome called attention to the confusion existing in the nomenclature of faults and noted that in the case of diagonal faults it is frequently impossible to say whether we are dealing with a normal or a reversed fault, or to determine whether a line at right angles to the fault-plane has been shortened or lengthened.2 The discussion which followed confirmed Mr Ransome’s statements. It also showed that the actual movements which have taken place in the case of faults in which there is a component parallel with the fault-strike have not been carefully studied, nor any methods described by which these movements could be determined; and a search through geological text-books and books on applied and field geology failed to discover more than a cursory treatment of this subject. I have for this reason thought it worth while to discuss the nature of . . .