Here's a breakdown:

* Deltas: Deltas are formed at the mouth of a river where it enters a larger body of water (like a lake or ocean). As the river slows down, it loses energy and deposits the sediment it has been carrying. This sediment builds up over time, creating a fan-shaped landform.

* Valleys: While not directly formed by deposition, valleys are often shaped and deepened by the deposition of sediment. Here's how:

* Erosion: Rivers erode the land as they flow, creating valleys. The eroded material is often carried downstream and deposited elsewhere.

* Deposition: Sediment carried by rivers can be deposited in valleys, especially when the river floods or changes course. This deposition can fill in low areas, widen the valley, and create terraces or floodplains.

So, while deposition is not the primary force creating valleys, it plays a crucial role in their formation and evolution.