Shabbat 7 - Special area called "karmelit"
Earlier we learned that there special areas on Shabbat which are neither public nor private, such as the sea. It is not private, because it is not surrounded by walls. Neither it is public, because public does not walk there. The Sages prohibited carrying objects on Shabbat in such areas, but since it is not a Torah prohibition, one is not liable for a sacrifice or a punishment if he carries there. Such areas are called "karmelit." What is the etymology of this word? Some say that it means "great forest." Others say that it means "ripe grain," which is in the intermediate state of being neither too moist nor too dry.
If there is a brick in the street, and one threw a sticky object on it, and it landed on the side of the brick, one has violated Shabbat - because this object as hanging in the air so close to the ground that it is considered to be on the ground. However, if the object landed on top of the brick, he is not liable, because it is a separate area, not part of the street, and people don't walk there - provided that is is taller than three hand-breadths. Rava said that even if the object landed on thorns and they are lower than three hand-breadths - he is not liable, since people don't walk on thorn-bushes. Rabbi Chiyya makes him liable even in the case of thorn-bushes, but not excrement. Finally, Rav Ashi makes him liable even when he threw an object on the excrement - because he says that anything that is lower than three hand-breadths is automatically part of the public area.
Art: Albert Bierstadt - The Shore Of The Turquoise Sea