Is this offline rendered? Or rendered in a 3d game engine? Or directly compositing in an editor(like photoshop)? If we knew that, we might could help better.

One thing that could apply regardless is to look at real life. Try to find pictures of a similar setting. See what it looks like is creating the separation in a similar setting in real life, and try to put that in there. Is there maybe a piece of wood between? Or maybe the train tracks are actually on cement instead of that rocky texture? Sand or grass running right up to a direct cutoff with cement could look real if done right, as that is how it is in real life. It might take some shadowing though, which would be done manually or done maybe in your 3d engine or offline rendering.

If you just make the top texture have a wiggly edge instead of a straight one, that should immediately make it look less artificial.

It looks like you need a sort of "Blend Map." The idea is that you create a gradient of sorts, but wiggly. The edges of the gradient would probably want to match up with the rocks so you don't cut rocks in half. It would work similar to splat maps.

If you are using 3dsmax, that indicates offline rendering to me. This would mean that you can afford to put more geometry, which would also very much solve your problem. Instead of just using a flat plane with tracks and rocks texture on it, I bet if you model the tracks, and either model the rocks, or use a displacement map based on that rocks texture, you will very much solve your problem.