Exploring the Grand Canyon, from the bottom up.

from Wikipedia:

scaleSize range(metric) Size range(approx. inches) Aggregate name
(Wentworth Class) Other names
< ’8 > 256 mm > 10.1 in Boulder
’6 to ’8 64-256 mm 2.5-10.1 in Cobble
’5 to ’6 32-64 mm 1.26-2.5 in Very coarse gravel Pebble
’4 to ’5 16-32 mm 0.63-1.26 in Coarse gravel Pebble
’3 to ’4 8-16 mm 0.31-0.63 in Medium gravel Pebble
’2 to ’3 4-8 mm 0.157-0.31 in Fine gravel Pebble
’1 to ’2 2-4 mm 0.079-0.157 in Very fine gravel Granule
0 to ’1 1-2 mm 0.039-0.079 in Very coarse sand
1 to 0 -1 mm 0.020-0.039 in Coarse sand
2 to 1 - mm 0.010-0.020 in Medium sand
3 to 2 125-250 m 0.0049-0.010 in Fine sand
4 to 3 62.5-125 m 0.0025-0.0049 in Very fine sand
8 to 4 3.90625-62.5 m 0.00015-0.0025 in Silt Mud
> 8 < 3.90625 m < 0.00015 in Clay Mud
>10 < 1 m < 0.000039 in Colloid Mud

Clastic sedimentary rocks, such as breccia or sandstone, were formed from rocks that have been broken down into fragments by weathering, which then have been transported and deposited elsewhere.Clastic sedimentary rocks may be regarded as falling along a scale of grain size, with shale being the finest with particles less than 0.004 mm, siltstone being a little bigger with particles between 0.004 to 0.06 mm, and sandstone being coarser still with grains 0.06 to 2 mm, and conglomerates and breccias being the coarsest with grains 2 to 256 mm. Breccia has sharper particles, while conglomerate is catergorized by its rounded particles. Arenite is a general term for sedimentary rock with sand-sized particles.