Our real and definite knowledge of the age of the lake-dwellings is hardly better. Hoops tells us that they belong to the Beech period of the Swiss flora. But this period may be much older in Switzerland than in Scandinavia; how much older we do not know. The underground stone burial-cysts of Switzerland look late. The small number of the villages containing no trace of copper and the high grade of household arts and technique in even the oldest of them suggest the same conclusion. Here again it seems dangerous to even conjecture a date. Montelius, whose opinion on these subjects is certainly of great value, says: "All things considered, I am convinced that the first stone graves were erected here in the north more than 3,000 years before Christ."[132] (It may be safe, therefore, to date them provisionally between 3000 and 4000 B. C.) "The epoch of the dolmens with covered entrance (_Gangräber_) begins about the middle of the third millennium B. C., and the epoch of the stone vaults or cysts (_Steinkisten_) corresponds to the centuries about 2000 B. C." CHART I. POSTGLACIAL STAGES RETREAT OF ICE AND CHANGES +----------------+---------------------+-------------------+----------------+ | | | PARALLELS IN | | | SCANDINAVIA | WESTERN AND | ASIA AND | DATE | | | MIDDLE EUROPE | ELSEWHERE[133] | | +----------------+---------------------+-------------------+----------------+ | | 1. Aachen Stage. | | 24,000 (to | | | | | 40,000) B. C. | | Ice-retreats in| Solutrean. Dry | | [134] | | northern | and Cold. | | | | Germany. | Steppe and | | | | | Tundra Fauna. | | | | | | | | | Swedish-Finnish| 2. Bühl Stage. | | 16,000 (to | | Moraines. | Early | | 24,000) B. C. | | | Magdalenian. | | [135] | | | Moist and cold. | | | | | Tundra. | | | | | | | | | Yoldia Period. | Middle Magd. | | | | Dryas Flora. | Steppe | | | | | Loess formed. | Susa founded. | | | | | | | | Glaciers in | 3. Gschnitz Stage. | Anau founded.[136]| 10,000 B. C.? | | Mountains.