What is stratigraphy?
Stratigraphy is a subset of geology and is the classification of layers (strata) of soil and rock.
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: What is stratigraphy?
### Input: 
### Response: Stratigraphy is a subset of geology and is the classification of layers (strata) of soil and rock.