Continuous animation

Dear Heroes, 

I'd like to create a funny 8bit like game and I'd like to create continuous scrolling background. I'd like to move the "ground" image from right to left. 

I am at the point where I am trying to move the large image like this: 

but: 

1) the animation is speeding up and slowing down

2) I'd like to loop it so it's constantly moving

Any ideas?