Breccias in general have been exhaustively discussed by W. H. Norton, and Bonney has fully described a large number of sedimentary origin. But since these papers were written attention has been drawn to certain fresh types of brecciated rock, and perhaps a briefer account than that in Norton's paper and one referring more particularly to British examples may be of service.

Some time before the war I examined the profiles, or longitudinal sections, of several rivers, with the object of ascertaining whether they tended towards any particular curve. The method of examination was similar to that employed by Professor O. T. Jones in his interesting paper on “The Upper Towy Drainage System”, but the data were obtained from maps and were not so exact as his. Some rivers showed a very close approximation to a catenary for the greater part of their course, but this was not the case with all. My final conclusion was that there is no general curve towards which all river-profiles tend the form is influenced by the rate at which the volume of the river increases downwards. No sufficient data, however, were available in the case of any river for the exact application of a general theory which was in my mind, and such approximations as were possible were too rough to be of any real value.

To reopen a question which has seemed definitely settled ever since 1898, and which has accordingly become an accepted opinion in geological circles, is neither a pleasant nor an enviable task. Yet, as the question is one of universal interest geologically, it has to be tackled and settled. In the following I intend to discuss the problem in a manner as objective and concise as possible, in order to concentrate the argument on the points which fundamentally govern the problem. As, from personal observations on the spot I am only familiar with the South African occurrence, I intend discussing that one only, however likely it be that the arguments brought forward may fundamentally affect the appreciation of other similar occurrences in South America and Asia.