Virchow has described a heap composed of mussel-shells on the outlet of Burtnecker Lake, east of Riga, called Rinnekalns.[33] Its most interesting feature is its pottery made of clay mixed with powdered mussel-shells, giving it a peculiar glitter. It is ornamented with lines arranged in an angular geometrical pattern encircling the vessel. Similar pottery can be followed far southward into Russia and westward as far as East Prussia, but not farther into Germany. Bored teeth used for ornaments occur. Bone implements are numerous, often ornamented with fine lines in zigzag or network. We find harpoons also. The flint industry was poorly and sparingly developed. Graves were discovered, but their contents proved that they belonged to a much later period. The culture is peculiar, paralleled to a certain extent but not repeated in western Europe. We still seem to detect the influence of a decadent, late Magdalenian style of ornament. Virchow considered them as very late Paleolithic or very early Neolithic. The shell-heaps of different regions resemble one another in general features, but differ and show their individuality in details of culture. These peculiarities may be due to difference of age or of culture or population, or to both. We must first attempt to find some place for them in the chronological succession discovered in France. They cannot be much older than the French period of transition, when Scandinavia first became habitable. But good cave-series covering the transition epoch are rare, and usually very incomplete. In 1887 Piette found a remarkable series in a cave or natural tunnel at Mas d'Azil, near Toulouse.[34] The most important strata were the following: 1. A dark layer evidently Magdalenian. 2. A yellow layer deposited by river floods. 3. Dark Magdalenian layer, with reindeer harpoons, engravings, and sculptures. Reindeer becoming rare; stag increasing. 4. Barren yellow layer, like 2. 5. Reddish layer (Azilian). No reindeer. Stag abundant. Flints nearly all of Magdalenian types. Flattened stag-horn harpoons perforated at base. Bone points and smoothers. Pointed flat pebbles. Bones of stag, bear, boar, wildcat, beaver. 6. Bones of wild boar, stag, horse. Flints similar to those in 5. Beginnings of pottery and of polishing; but not of polished axes. Piette's Arisian. Beginning of Neolithic. 7. Neolithic and Bronze remains. Layer 5 evidently represents a period posterior to the Magdalenian and anterior to the real Neolithic. Hence Piette considered it as marking a distinct Azilian Epoch, resembling the Magdalenian in most of its flint implements, in the absence of pottery and of polished axes. But the reindeer has here given place to the stag, and the harpoon has changed correspondingly and is less skilfully made. Bone implements are decadent.