Final answer:
Sand indeed blows up the windward side of a dune, accumulating on the slip face, making the statement true. This process of sediment movement creates cross-bedding, indicating past wind or water directions.
Step-by-step explanation:
The statement that sand blows up the windward side of a dune or ripple and then accumulates on the slip face is true. The windward side is the side of the dune that faces the incoming wind and is typically gentler sloping. The sand grains are transported up this slope by the wind.
When they reach the top, they tumble down the steeper 'slip face' on the other side, which faces away from the wind. This process is called saltation, and it results in the migration of dunes in the direction of the prevailing wind.
Over time, as sediment continues to move and deposit, features like cross-bedding can form, showing geologists the historic direction of wind or water flow.