The main idea of this paragraph is that the rocks cannot be explained by science, that there is a mystery to them. This sentence contributes to that idea because it gives a specific example of one of the odd things about the rocks. Because they are on a flat surface they should not roll or move on their own, but the fact that they have a trail behind them shows that they have somehow moved. This supporting statement is then supported by more details about the trails.
Answer:
you can't answer that without the paragraph
Why is friday the 13th called bad luck day?
Friday the 13th sucks a.ss . Like real f.u.cking a.ss
the end
