Conglomerates

Conglomerates: Clastic rocks consisting of rounded or sub-rounded fragments, implying rather more transport than breccias. The following are the main types of conglomerate:

1. Those consisting essentially of one type of pebble, usually quartz and/or chert pebbles - oligomict;
2. Those consisting essentially of a mixture of pebble types - petromict or polymict;
3. Glacial conglomerates, tillites, consisting of a mixture of rock pebbles and rock flour;
4. Those formed by the break-up, in situ, of a previously deposited deposited layer of rock - intraformational or authochthonous conglomerates.

Modern pebble accumulations, such as beaches, flood plains, and outwash fans, may become conglomerates when cemented.