Final answer:
The B horizon is the uppermost limit of the zone of accumulation and is considered the subsoil, while the A horizon is considered the topsoil.
Step-by-step explanation:
The soil horizon that represents the uppermost limit of the zone of accumulation, also known as the subsoil, is the B horizon. The B horizon is a soil layer that has primarily accumulated fine materials that have moved downward, enriching this layer compared to layers above it.
While the A horizon is rich in organic matter and is considered the topsoil, the B horizon's composition makes it denser and distinct in physical and chemical properties. Therefore, it is essential in understanding soil profiles in the context of agriculture, civil engineering, and environmental science.