Cobbles

Primitive paving stones. Several classic races in the spring are run over roads paved with cobbles, most notably the Paris-Roubaix.
Found on http://cycling.isport.com/cycling-guides/cycling-glossary

cobbles

Rock fragments 7.6 cm (3 inches) to 25.4 cm (10 inches) in diameter.
Found on http://www.encyclo.co.uk/local/22040
No exact match found