Cases of relatively recent change in the courses of rivers, due to the invasion of their valleys by neighbouring and more rapidly working streams and the consequent diversion of their waters, have been investigated of late years by an increasing number of geologists in different countries. Such phenomena are, of course, most frequent in mountain districts, and the Swiss Alps have yielded many examples of greater or less certainty. Some cases are evident and undeniable; others are difficult to decide upon, and need careful consideration of all available evidence; while in yet other instances it is possible that statements as to the occurrence of such changes have been accepted on inadequate authority. The generally received opinion as to the present and past relationship of the Landwasser and the Landquart can certainly not be included in the last category, but neither can it, I think, be rightly placed in the first.