But in spite of these difficulties, attempts have been made from time to time to determine the absolute chronology of these ages. The results, however, can only be considered as approximations of the truth. We will call attention to some of these calculations. Their value to us consists in showing us the methods by which this problem has been attacked, and not in the results obtained. M. Morlot, of Switzerland, has sought to determine this question by a study of the delta of the Tinière, which is a small river flowing into the lake of Geneva. Like all mountain streams, it brings down considerable quantities of sediment, with which it has formed a conical shaped delta. Cuttings for a railroad exposed a fine section of this cone, and showed that at three different times layers of vegetable soil, which must once have been its old surface were found. The lowest surface was some twenty feet beneath the present surface, and here were found relics of the Stone Age. The second layer was at the depth of ten feet, and contained relics of the Bronze Age. Finally the first buried layer, three feet beneath the present surface, was found to contain relics of the Roman Age. Obtaining from other data the time that has elapsed since the deposits of the Roman layer, he readily calculates the age of the Stone and Bronze layers. By this means he obtains for the Bronze Age an antiquity of between three and four thousand years, and for the Neolithic Age from five to seven thousand years.17 M. Morlot does not claim for his calculation more than approximate accuracy.18 But if we were to allow it a greater accuracy than its author claims, it would still only show us that from a period of from five to seven thousand years ago, tribes of stone using folks lived in Switzerland. It tells us nothing as to their first appearance, or the total length of this age.19 Other calculations of a similar nature have been made. The Lake of Bienne, in Switzerland, has been gradually silting up along its margins from time immemorial. About seven hundred and fifty years ago there was an abbey built at one place on the then existing shore of the lake. Since that time the gain of land has been about twelve hundred feet. A considerable distance further up the valley are found the remains of a lake settlement of the Stone Age. If the gain of land has been uniform, it has not been far from seven thousand years since the lake washed round the ancient settlement. Of course the land may have gained faster at one time than at another, but from the general configuration of the valley it is considered that its gain was regular.20