Questions: Which type of unconformity is usually easiest to spot, since layers are on top of nonlayered crystalline rock?

The answer is the fourth one (Nonconformity): layers are on top of nonlayered crystalline rock.

Explanation for each option:

1. Disconformity: This type of unconformity occurs between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition. It is not necessarily easy to spot because the layers are parallel and can be difficult to distinguish without detailed study.

2. Paraconformity: This type of unconformity is a subtle one where there is no obvious erosion surface or angular discordance between the layers. It is often difficult to identify because the layers are parallel and there is no visible gap.

3. Angular unconformity: This type of unconformity occurs when horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers. While it can be noticeable due to the angular difference, it is not as straightforward as nonconformity.

4. Nonconformity: This type of unconformity is the easiest to spot because it involves sedimentary rock layers deposited on top of nonlayered crystalline rock (such as igneous or metamorphic rock). The stark contrast between the layered sedimentary rocks and the nonlayered crystalline rocks makes it more apparent.

Summary: Nonconformity is usually the easiest type of unconformity to spot because it involves sedimentary layers on top of nonlayered crystalline rock, creating a clear and noticeable contrast.