Pebbles seen on the beach are of different type. Some of these are volcanic, some non-volcanic while some are granite. These pebbles have come from the bedrock lying next to the beach. Each rock seen on the beaches had once been a part of the bedrock before it broke down and became an individual entity and so were these small pebbles.
Thousands of years ago as the glaciers melted, they hit the bedrocks and several small stones of different shapes and sizes were formed each time they did. These stones eventually got settled on the sea shores. As they came into contact with the sea waves and rolled up and down numerous times, they became more refined and rounded. These polished stones are commonly known as pebbles.