Answer:
The rock layers are initially formed in a horizontal manner as the sediments are deposited over one another, forming horizontal rocks.
But these rock layers are not always found to be horizontal. They are sometimes tilted. This is due to the compressional stress that acts on the rock layers from both sides, which results in the tilting, faulting, and folding of the layers.
In addition to this, these layers are sometimes eroded due to the agents such as wind, water, and ice, and so these layers are not found to be horizontal.