Why is a high bit of land called a low?

It just is, that's all. From an old word hlaw or similar, which means mound or hill. We moved in December, quite near to Werneth Low. Hence getting lost walking poems, like this one.

29^th January 2016

This morning lost on Werneth Low, just couldn’t find which way to go.
Tweaked my knee on awkward stile, still I had to walk for miles.
Why’s it called a ‘low’? It’s steep! And covered with aggressive sheep
Which ran straight at us. Bloody hell! And suddenly my knee was well.
I reckon there were almost fifty; we exited their field damn nifty. 
The arrows led me there and then the footpath disappeared again.
So out of farmyard gate we go’ed and had to walk along the road.
Blimey, don’t those cars go fast, we hid in hedge as each went past.
A footpath with a sign, hooray! To Stockport – no, that’s the wrong way.
Had to stay on tarmac black and hope the road would take us back.
Yes, we made it home again, but not before caught in the rain.
Breakfast for the dog; and me? of course, I’ve got a cup of tea.
Sermon to write – naa, there’s a laugh. I’m going to run myself a bath.