Agglomerate

Agglomerate, or VOLCANIC AGGLOMERATE, is a rock made up of a confused mass of angular and subangular blocks of all sizes. The blocks may consist exclusively of igneous rocks, or of sedimentary rocks, or of both, set in a more or less meagre matrix of finer-grained detritus of the same materials. The rock is of volcanic origin, and is frequently found in Scotland filling up vertical holes or pipes which seem to have been the throats or necks of ancient volcanoes.