Boulders

(1) Rock fragments more than 10, 25, or 50 cm in size, depending on the classification. Often, 1 m is taken as the upper limit for boulders (larger fragments being called blocks). Sometimes the term is applied only to spherical or rounded fragments.

Boulders are a major component of psephitic rocks (pebbles, shingle, and conglomerates); they occur frequently in alluvium and proluvium of mountainous countries and in glacial deposits. They are used under the name cobble (rubble) in the paving of roads and the production of crushed stone.

(2) Glacial boulders are rock fragments, irrespective of size, picked up and transported by glaciers; they are often rounded, polished, and covered with scratches (glacial striae). They occur in moraines and in glaciofluvial deposits. They are sometimes found in large quantities in areas of former glacial activity.