Given the same rock thickness and amount of rainfall, which rock type is most susceptible to dissolution?

The rock type most susceptible to dissolution in this context is a jointed mass of limestone. This is primarily due to the chemical properties of limestone, which is primarily composed of calcium carbonate. When rainwater, slightly acidic due to dissolved carbon dioxide, comes into contact with limestone, a chemical reaction occurs that can lead to dissolution. The presence of joints or fractures in the limestone enhances its susceptibility because these openings allow rainwater to infiltrate more easily, thus increasing the surface area exposed to dissolution processes.

In contrast, granite, while it can weather physically, is significantly less prone to chemical dissolution due to its composition of quartz and feldspar, which are much more resistant to chemical weathering. Compacted clay layers offer minimal dissolution potential since they consist of fine particles that do not typically dissolve in water. Sandstone, composed mainly of sand-sized grains, can experience weathering and erosion but is less susceptible to dissolution compared to limestone, as it typically does not react chemically to water in the same way. Thus, the jointed mass of limestone stands out as the rock type most at risk for dissolution under the conditions described.