the rock wears out
Rocks and pebbles are made out of bits of rock that has been cut down from mountains etc.
pebbles
The small pebbles are more likely to fall through the gaps between bigger pebbles than the other way around.
Pebbles Flinstone
One common technique used to separate pebbles and sand is sieving. By passing a mixture of pebbles and sand through a sieve with appropriate mesh size, the smaller particles such as sand will pass through while the larger pebbles will be retained on top of the sieve.
Filtration will separate the pebbles and water ... Pour the mixture through a strainer (or better yet, an old burlap bag) and catch the water in a bucket. The pebbles will remain in the strainer or bag.
Pebbles are often found at the top of a beach because they are lighter and get washed up by waves and tides. The force of the water can carry the pebbles to the upper parts of the beach as it recedes. This process of wave action and erosion tends to concentrate smaller, lighter materials like pebbles at the higher points of a beach.
the Atlas Mountains
Pebbles - Pebbles album - was created in 1986.
The top mountains are 1. Tahat 2. Tinra 3. Tizouyadi
Pebbles sung Girlfriend in 1988.
One way to separate pebbles from soil is by using a sieve. Pour the soil and pebbles mixture onto the sieve and shake it gently. The pebbles will remain on top of the sieve while the soil passes through. Another method is to handpick the pebbles from the soil manually.