"The Teachings of the Midewiwin were scratched on birch bark scrolls and were shown to the young men upon entrance into the society. Although these were crude pictographs representing the ceremonies, they show us that the Ojibwa were advanced in the development of picture 'writing.' Some of them were painted on bark. One large birch bark roll was 'known to have been used in the Midewiwin at Mille Lacs for five generations and perhaps many generations before',  and two others, found in a seemingly deliberate hiding place in the Head-of-the-Lakes region of Ontario,  were carbon-dated to about 1560 CE +/-70.  The author of the original report on these hidden scrolls advised: "Indians of this region occasionally deposited such artifacts in out-of-the-way places in the woods, either by burying them or by secreting them in caves. The period or periods at which this was done is far from clear. But in any event, archaeologists should be aware of the custom and not overlook the possibility of their discovery."