Here's the breakdown:

* Soil and rock debris DO accumulate on the continental slope. This material is called sediment and originates from various sources, including erosion from the land, weathering of the continental shelf, and even biological activity.

* Ocean currents DO play a role in moving sediment. They can transport sediment along the coast, but they usually don't directly "wash" it down from the land.

* Gravity is the primary force behind sediment movement down the continental slope. Once the sediment reaches the continental shelf edge, gravity pulls it downslope, creating turbidity currents. These dense, fast-moving flows carry vast amounts of sediment down the slope, depositing it in deeper water.

Therefore, while ocean currents contribute to sediment transport, it's primarily gravity and turbidity currents that drive the accumulation of soil and rock debris on the continental slope.