Evidence of a like character is found in a number of facts cited by Venetz in his celebrated paper upon the variations of temperature in the Swiss Alps, drawn from the parish and commune registers of the Canton of Valais. Among these are acts concerning the right to roads which are now either entirely hidden by ice, or rendered nearly useless by the advance of the glacier, a lawsuit respecting the use of a forest which no longer exists, but the site of which is covered by a glacier, and other records of a similar character. The only document, so far as I know, previous to this century, which furnishes the means of delineating with any accuracy the former boundary of a glacier, is a topographical plan of the environs of the Grimsel, including the extremity of the Aar, making a part of Altmann's work upon the Alps. In 1740, Kapeler, a physician of Lucerne, undertook a journey to the mountains of the Aar, to visit certain crystal grottos, now well known, but then recently discovered. He prepared a map of these grottos and their vicinity, in which they are represented as being situated at some distance from the extremity of the glacier, the lower end of which is now considerably beyond them.[50] But to return to the glacier of the Rhone. We can detect the sequence and relative age of its ancient moraines, not only by their position with reference to each other and to the present glacier, but also by their vegetation. The older ones have a mature vegetation; indeed, some of the largest trees of the valley stand upon the lower moraines, while those higher up, nearer the glacier, have only comparatively small trees, and the more recent ones are almost bare of vegetation. Moreover, we do not lose the track of the great glacier of the Rhone even when we have followed its ancient boundaries to the shores of the Lake of Geneva; for along its northern and southern shores we can follow the lateral moraines marking the limits of the glacier which once occupied that crescent-shaped depression now filled by the blue waters of the lake.