Perfectly normal - I have seen that feature many, many times.
You really need to learn some astronomy.
I guess you have never heard of the 'straight wall'?
it is a fault line on the surface of the Moon, known as 'Rupes Recta' - and is situated in the Mare Nubium.
There are several of these faults (sometimes called 'rilles') on the surface of the Moon, but Rupus recta is the most well known.
Ask any experienced Moon-watcher, and he/she will know about it.
It is one of the objects in the 'Lunar 100' observing challenge for Moon viewers.
(L-100 no.15 to be exact)
If you think the straight wall is amazing - you should look up 'Purbach's cross', then view it through a telescope (timing is critical)
It would blow your tiny mind.