Fig. 1.14. Transportation of different size fragments

Sedimentary rocks are deposited in layers as strata, forming a structure called bedding. The study of sedimentary rocks and rock strata provides information about the subsurface that is useful for civil engineering, for example in the construction of roads, houses, tunnels, canals or other constructions. Sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores. Based on the processes responsible for their formation, sedimentary rocks can be subdivided into groups.

1. Clastic sedimentary rocks are composed of silicate minerals and rock fragments that were transported by moving fluids (as bed load, suspended load, or by sediment gravity flows) and were deposited when these fluids came to rest. Clastic rocks are composed largely of quartz, feldspar, rock (lithic) fragments, clay minerals, and mica; numerous other minerals may be present as accessories and may be important locally (Báldi 1991, Szakmány 2008a). Clastic sediment, and thus clastic sedimentary rocks, are subdivided according to the dominant particle size (diameter). These are gravel (>2 mm diameter); sand (1/16 to 2 mm diameter); mud (clay is <1/256 mm; silt (is between 1/16 and 1/256 mm) (Table 1.1.).

Grain size (mm)	incoherent debris	cemented rocks
>256	boulder	coarse grained rocks: conglomerate breccia
64-256	coarse grain gravel
4-64	gravel
2-4	fine grain gravel
1-2	coarse grained sand	sandstone
0,5-1	semi-coarse grained sand
0,25-0,5	medium-grained sand
0,125-0,25	small-grained sand
0,063-0,125	fine grained sand
0,031-0,063	coarse grained aleurite	aleurolite	"mudrock"
0,016-0,031	medium-grained aleurite
0,008-0,016	fine grained aleurite
0,004-0,008	very fine grained aleurite
<0,004	clay	clay stone

Table 1.1. Classification of siliciclastic rocks on the base of their grain size (Szakmány 2008)

Subdivision of these three broad categories is based on differences in clast shape (conglomerates and breccias), composition (sandstones), grain size and/or texture (mudrocks).

Extrabasinal sedimentary rocks can be arise both marine and continental environments. Size, roundness and sorted of grains signed the original environment (1.16., 1.17. ábra).