Returning to the Baltic region,[110] we find that a cave on the island of Stora Karlso, close to the west shore of Gothland, contained Neolithic deposits nearly three metres thick. In the upper layers there were remains of domestic animals, in the lower only wild forms. This island lies some thirty miles from Oland, just off the east coast of Sweden. Montelius tells us that before the end of the Neolithic period there was communication between Sweden and Finland, as well as with Denmark and Germany; that trade between these regions was active, and that there is reason for thinking that there was communication between the west coast of Sweden and England. It seems highly probable that boats were creeping along the coast of Spain and France from harbor to harbor, although the evidence is here less clear and compelling. Our knowledge of Neolithic boats is still very incomplete.[111] Those of the lake-dwellers seem to have been usually hardly more than dugouts hollowed by fire. One, however, from Lake Châlain (Jura) was about thirty feet long and two and one-half wide, made out of an oak-trunk. Such boats served well for river navigation, but were too shallow and clumsy for the open sea. It would have been a comparatively easy matter to add one or two planks along each side of such a dugout and thus build up a fairly seaworthy craft. The rock-sculptures of Bohuslan, Sweden, which probably date from early in the Bronze Age, represent boats of fair size carrying as many as thirty men.[112] The wares exchanged in this trade were limited in material and value. Metals and metallic objects were still unknown, except as copper and gold came in before the end of the period. Still, there were many objects which met a fairly wide demand. We have already seen that different lake-dwellings differed markedly in their products. Some were almost purely agricultural. In others we find remains of pottery evidently manufactured on the spot in larger quantities than the village could use. Much of this must have been exported along the lake, perhaps farther. Schliz distinguished at Grosgartach a rude home-made pottery from a finer ware apparently brought from some centre of finer and more artistic work. The Neolithic housewife was probably very proud of this "china." The finer grades of cloth manufactured at Robenhausen and elsewhere were probably carried far and wide, but it is impossible to trace it. The flint mined at Grand Pressigny was transported to greater or less distances, as well as manufactured at the mouth of the mine. At the various workshops the implements were made in great numbers and still more widely disseminated. This was equally true of flint regions in other parts of Europe. Stone arm-rings, mace-heads and other fine articles found sparsely in northern Europe may well have been copies of a few articles brought from Italy or even farther.[113]