Siltstone is a sedimentary rock made up of silt, silt is a term used for clay and is very fine grained. The size of the grains ranges from 1/256 to 1/16 millimetre. The siltstone is very similar to sandstone in appearance but indeed has very fine texture. The grains when deposited becomes compact and cemented together into a solid stone. The cementing material in silt stone is silica, calcite and iron oxides. The cementing material fills the pore spaces between the silt grains by water. It takes million of years for the cementing material to fill up the spaces and results in a solid stone.