iPhone mesh renderer performance

Well , I am new to Unity3d. I generated a 2d terrain with a mesh filter with mesh renderer and mesh collider. At first it goes very well, but after 15minutes or less, the texture becomes weird. There are the two pictures here.6922-11111.png

6926-22222.png

Anyone knows how to deal with this ? Thanks !

I guess i solved it by myself. This happened because of the uv coordinats. The uv coord of iphone should be between 0…1 , if it is too large, it will be like the picture in the question.