[With regard to] a field in which a grave was lost, and a house with an upper story was built on it: if the doorway of the upper story was directly above the doorway of the house, the upper story remains tahor. But if not, the upper story becomes tamei. Soil of a beis hapras and soil from outside the Land of Israel that arrive in veg-etables combine when there is as much as the seal of packing sacks, these are the words of R’ Eliezer. The Sages say: Only when the amount equal to the seal of packing sacks is in one place. R’ Yehudah says: It used to happen that letters came from overseas to the sons of Kohanim Gedolim and they had on them the equivalent of a se’ah or two of seals — yet the Sages were not concerned that they might be tamei.