That there is a wide-felt want, among field-geologists, of some rapid and sufficiently accurate method of solving such problems as arise in the ordinary course of their work is proved, if proof were necessary, by the summary of the literature bearing on this subject, given in the April Number of this Journal by Mr. Harker, who has certainly carried it to its highest point, for methods more simple than those given by him it is impossible to imagine. There is, however, a method, by which most of these problems can be solved by inspection without recourse to construction or calculation, which I would submit to the notice of geologists in general