When a tariff-ic idea in the Stone Age left every OG and Magog stone broke

'A tariff,' explained the magus, 'is something that is imposed as a supposedly corrective measure to deter trade imbalances. For instance, Magog 1 can impose a 25% tariff on Og 1, whereby for every boulder weight of roots and berries and wood that Og 1 supplies, Og 1 has to accept 1.25 boulder weights of woolly mammoth from Magog 1.