Figure 1 illustrates a geological block diagram used to practice determining the relative ages of rock units, including sedimentary layers and igneous intrusions.

To determine the relative age of each rock unit in the block diagram and list them in order from most recent to oldest, we need to apply principles of geology, particularly the law of superposition and the principle of cross-cutting relationships. Let's analyze the image step by step.

Step 1: Understand the Block Diagram

The block diagram shows a sequence of rock layers and features such as erosion surfaces, dikes, and intrusions. Here are the key observations:

- Horizontal Layers: The horizontal layers represent sedimentary rocks deposited over time.
- Erosion Surfaces: These indicate periods of erosion where older rock layers were removed before new layers were deposited.
- Intrusions: Igneous rocks (e.g., dikes, pegmatite) that cut through existing rock layers are younger than the layers they cut.
- Dikes: Vertical igneous bodies that cut across existing rock layers.
- Pegmatite: A type of igneous rock that forms from magma cooling slowly underground.

Step 2: Apply Geologic Principles

#### Law of Superposition
- In undisturbed sequences of sedimentary rocks, the oldest layers are at the bottom, and the youngest layers are at the top.

#### Principle of Cross-Cutting Relationships
- Any geologic feature that cuts across another is younger than the feature it cuts.

Step 3: Analyze the Rock Units

Let's identify and order the rock units based on these principles:

1. Shale and Siltstone: These are at the very top of the sequence and are therefore the youngest.
2. Volcanic Ash: This layer is below the shale and siltstone but above the erosion surface. It is younger than the erosion surface but older than the shale and siltstone.
3. Limestone: This layer is below the volcanic ash and is cut by the erosion surface. It is older than the volcanic ash.
4. Sandstone: This layer is below the limestone and is also cut by an erosion surface. It is older than the limestone.
5. Slate: This layer is below the sandstone and is cut by the pegmatite intrusion. It is older than the sandstone.
6. Granite: This layer is below the slate and is cut by the pegmatite intrusion. It is older than the slate.
7. Basal Dike: This dike cuts through the granite, slate, sandstone, and limestone. Since it cuts across these layers, it is younger than all of them.
8. Pegmatite: This intrusion cuts through the granite and slate. Since it cuts across these layers, it is younger than the granite and slate but older than the basal dike.

Step 4: Order the Rock Layers

Now, let's list the rock layers in order from most recent (top) to oldest (bottom):

1. Shale and Siltstone
2. Volcanic Ash
3. Limestone
4. Sandstone
5. Slate
6. Granite
7. Pegmatite
8. Basal Dike

Final Answer:

\[
\boxed{\text{Shale and Siltstone, Volcanic Ash, Limestone, Sandstone, Slate, Granite, Pegmatite, Basal Dike}}
\]