How Could Sheep Graze these Steep Hillsides Without Leaving any Marks? Here are two images of English hill figures (The Cerne Abbas giant and the Uffington white horse):



These hillsides, which are obviously grazed by sheep, show tracks that form numerous contour lines around the said hillsides. According to many people, however (e.g., Wikipedia), these contour lines are not generated by domestic livestock.

If that is the case, what causes these lines and why do they only appear on hills that are grazed by livestock? If, on the other hand, no livestock grazes these pastures, what keeps the grass so short and why are English farmers wasting such huge amounts of good grazing land? Are they mad? Some people, such as this answer, say the lines are caused by natural earth movements, but won't explain why they only occur on hills that are grazed by livestock. There are many more examples, and better ones, of chalk hill contour lines available on Wikipedia, but my simple explanation of how to find them has been deleted. The Long Man of Wilmington is a much better example than the two photos above, it shows the sheep as well as contour lines and is available on Wikipedia.
Those lines have nothing to do with animals.

Those lines are generated by solifluction and frost heave. It is sometimes referred to as cryoplanation or soil creep. Basically as the thin hillside soil freezes and thaws it expands and contracts and because there is a slop it moves downslope. In addition rain combined with how the surface thaws before the deeped ground causes a plane of weakness and movement. It can form a variety of patterns but on strong slopes it tends to form stripes or ripples. 

That area of England is well known for such landform. Below is a picture from Dorset and another from the isle of wight. They don't only occur on grazed ground, but if ground has trees they act as anchors for the soil and you don't get the more noticeable lines and nobody is going to graze animals on ground with nothing but trees or hills with no soil which also will not have them. 

 



1. Sugden, David E. (1971). "The significance of periglacial activity on some Scottish mountains"

2. frost creep and gelifluction features a review