The coarsest-grained sedimentary rock is called conglomerate. It contains particles larger than sand, although it may contain finer particles, too. It looks very much like concrete. One variety is called pudding stone, from its resemblance to a pudding studded with fruit. In fact, the gastronomy-minded French use the word poudingue for conglomerate. The pebbles and rock fragments are usually cemented together by calcite or quartz. If the rock is made up of rounded pebbles, it is called conglomerate; if the pieces are broken and angular, it is breccia.

Waves and currents strong enough to drag in pebbles and whisk away sand and silt are also strong enough to break up potential fossil material that becomes mixed with the gravel. A conglomerate layer formed in this way is usually poor hunting ground for fossils, although it may contain pieces of petrified wood, bone, coral, or tough shells. But while crossing areas where conglomerate occurs, look for fossils in the pebbles themselves; you may make a rich haul.

Mixed Conglomerate

Coarse-textured conglomerate is a poor medium for preserving fossils.

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  • edna
    What fossils are in conglomerate?
    8 years ago

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