As stated in Graphic Design the New Basics, texture can be achieved by layering various material on top of one another. Often times they are overlapped in a way that makes them look seamless and meant to be clustered in a more natural way, however recently some artists have been making the layering process obvious to give transparency and give a different take on the concept of texturing via layers.
In Lynda Barry’s book on the 4th page i noticed an immense amount of layering. It looks like she painted watercolor on the original paper and then pasted bits of other pieces of paper on top of the paintings themselves. She also talks about how one form can change into another, and adding alternating mediums with varying textures can definitely ad to the feel of change she was trying to convey.