CONGLOMERATE
Colour Variable.
Texture Consists of rounded pebbles (diameter greater than 2 mm),
cobbles or boulders set in a fine- or medium-grained matrix.
Structure Bedding absent or only crudely developed; may be apparent
from variation in the size of the pebbles. Fossils rare.
Mineralogy Pebbles, boulders etc. may consist of quartz, chert,
flint or almost any igneous, metamorphic or sedimentary rock,
but tougher rocks such as quartzite often predominate. The matrix
usually comprises sand or silt, often cemented by silica or calcite.
Field relations Conglomerates are consolidated pebble, gravel
or boulder beds which accumulate along sea and lake shores and
in rivers. They are indicative of shallow water sedimentation
and vigorous currents, which are required to move large rock fragments.
Marine transgressions (rise of sea-level with consequent flooding
of the land) are frequently marked by conglomerates which, therefore,
are often found immediately above unconformities. Conglomerates
are usually associated with sandstone and arkose." (Hamilton
et al 1976, 192)
