The part of a belt that transmits power and carries the load is:

The carcass of a belt is the component that serves as the backbone for power transmission and load carrying in belting applications. It consists of multiple layers of fabric or material that provide strength and structural integrity to the belt, allowing it to withstand the tension and mechanical stress encountered during operation. The carcass is crucial for maintaining the belt's shape and ensuring efficient power transfer from one pulley to another.

In contrast, the other options do not primarily serve the function of load carrying or power transmission. The camber slide typically refers to a design feature that affects the belt's alignment, while the breaker ply is a layer that adds toughness and prevents belt separation but is not the main component that transmits power. The skin, often referring to the outer layer of the belt, provides protection and wear resistance but does not directly carry the load in the same way the carcass does. Hence, the carcass is the accurate choice as it embodies the essential functionality for power transmission in belt systems.