(Mishnah): One should not open a stone quarry in his field (otherwise it appears as if he is preparing his field for planting) unless it has three visible layers of stones that are three by three and three high. He is then permitted to remove 27 stones.

If there's a wall that has at least 10 stones, each heavy enough to require 2 men to carry them, he may remove all of the stones from the wall.

The minimum height of the wall (to be able to remove stones freely) is 10 tefachim. If it's less than that or there aren't 10 large stones, it is like a quarry and he may cut from it until it is a Tefach from the ground.

When is it prohibited to remove stones from a quarry or wall? When he's taking them from his own field, but he may take whatever he wishes from his friend's field.

It is also only prohibited if he did not begin before Sheviis, but if he did, he may continue to take without limit.

(Gemara): How are the 27 stones arranged? Three rows of nine stones or nine rows of three stones.

Baraisa: A quarry that is partially in a person's field and partially in his neighbor's field; if his neighbor opened a quarry in a permitted way, he may continue it. But if it was completely cleared out, it is prohibited.

Mishnah in Maseches Ohalos: A Ziz (a decorative board protruding from a house wall above a doorway) can bring Tumah (to the entire house) even if less than a Tefach wide (as it joins with the width of the house wall); a Gizrah (a board whose end is bent upwards) and a Govlis (that bends upwards on each side like a gutter) - both bring Tumah if they are a tefach wide. (The Mishnah there then continues to explain that the Ziz is three rows higher than the doorway.

(R. Chanan bar Abba): This means that a person who agrees to make a row of stones for his friend, must make it a height of 4 tefachim.

Support (R. Yosi): That Mishnah (in Ohalos) teaches that - 'When did they say that the Ziz of any width brings Tumah? If it is 3 rows above the doorway, which is 12 Tefachim. Why did it teach 'rows'? To teach how many Tefachim there are in a row.

Question (R. Chiya bar Abba): Is the measure of stones for the fence in our Mishnah the same as that of the rows discussed in Maseches Ohalos?

Answer (R. Chezkiyah bar Yaakov bar Acha citing R. Yosi ben Chanina): They are the same.

Question: But here the minimum height of the wall is 10 Tefachim and in Tumah, it is 4 Tefachim...?

Question: What's the case of our Mishnah? If there are two rows, it should be 8 Tefachim; if there are three rows, it should be 12 Tefachim?!

Answer (R. Yosi): There are 3 rows, but since at any point of contact between the rows, he must file and smooth each stone 1/2 a Tefach, so a total of 2 Tefachim is filed down and the height of 3 rows is therefore 10 Tefachim; less than 10 is not a wall or a quarry.

Baraisa (R. Yehuda): When must he leave a Tefach above the ground? When he is intending to improve his field for planting, but if not, he may cut even more and does not need to leave a Tefach.

(Rabban Shimon ben Gamliel): When may he remove stones and leave a Tefach? When he isn't intending to improve his field for planting, but if he is, to remove even less than that is forbidden.

(R. Baybei): R. Yasa ruled leniently like this Baraisa (like the opinion of R. Yehuda).