The Greenway

Barley, a dog, follows a trail of moss down an inclined sidewalk.

Another quality fostered by hills are very specific moss formations. Note how a channel seems to be cut right along the edge of the concrete, beyond which moss suddenly flourishes and then peters out. I speculate that this pattern is the specific result of rain runoff. The runoff is frequently enough that it prevents the moss from encroaching any further to the left, but the runoff itself has been enriched by the yards from which it has overflowed, so it also encourages moss growth. This results in a sharp boundary, whose sharpness narrows and channels the runoff. To the left, currents too strong for outgrowths to get purchase; to the right, a ridge that draws from the current as Egypt did from the flooding of the Nile.