A pitted ware pottery shard, <a href="//commons.wikimedia.org/wiki/Category:Uppland" title="Category:Uppland">Uppland</a>, Sweden
Nordisk familjebok
1917
<a href="//commons.wikimedia.org/wiki/Nordisk_familjebok" title="Nordisk familjebok">Nordisk familjebok</a> (1917), vol.26, <i>Till art. Stenålder. II.</i> <a rel="nofollow" class="external autonumber" href="http://runeberg.org/nfcf/0686.html">[1]</a>