For 500 Million years the Jungfrau-Aletsch region has been scene of a constant geological and geographical evolution. The Alps are still rising approximately 0,5 to 0,7 millimetres per year, faster than the rate of erosion. This is due to the northward drift of the African tectonic plate, pushing against the stable Eurasian plate at a rate of 5 centimetres per year. The formation of the Alps, between 20 and 40 million years ago, is a consequence of the collision of these two plates. The resulting over thrusts and upward thrusts have led to complex formations. The chronology of the geological layers is often surprising since the oldest layers are not always at the lowest levels, where they normally are, but lie on top of more recent ones. Thus the peaks of the Mönch and the Jungfrau consist of a crystalline rock which is older than the limestone below, whereas the summit of the Eiger is almost exclusively limestone. This complexity can also be deduced from the physiography of the region: The north is distinguished by precipitous walls of rock including the renowned North Face of the Eiger with its 1,800 meter sheer drop and steep valleys. In the South the slopes fall more gently towards the Rhone Valley. This tells us that, considering the history of the Earth, the Alps as we know them are among the more recent mountain formations, since they are only 2 million years old.