A Classification of Sedimentary Rocks

Inorganic origin:
1. Coarse fragmentary material resulting from weathering talus
2. The same fragmentary material cemented breccia
3. Unsorted material resulting from rock weathering soil
4. Coarse fragments rounded by the action of water and wind gravel
5. The same material cemented conglomerate
6. Finer material deposited by water or wind sand
7. The same material cemented sandstone
8. The finest material, mostly kaolin, deposited by water clay
9. The finest material, deposited by wind loess
10. The same material cemented shale
11. Fine particles of lime, pure or impure marl
12. The same material cemented limestone
13. Unassorted material left by the glacial ice till
14. The same material cemented tillite
Organic Origin:
15. Limes made from shells, etc. coquina, chalk, coral rock, etc.
16. Silica from the shells of plants, etc. diatomaceous earth, etc.
17. Carbon from plants peat, lignite, coal, etc.
18. Hydrocarbons from animals petroleum, asphalt, amber, etc.
19. Phosphates from animals guano, phosphate rock, etc.

[Talus]

Where weathering is very active, especially on or below steep mountain slopes, a mass of loose, angular fragments accumulates. This material is termed talus, a term which refers only to the physical character of the material, and not at all to its composition. If weathering continues these fragments will be further broken up into one of the finer grained rocks, which the water can carry away and deposit elsewhere. There is little or no layering in talus. If the talus is not carried away but is cemented where it was formed, the resulting mass is termed breccia, but this is not very commonly the case.

[Breccia]
[Pl. 58]

The term breccia is used to cover all those rocks which are composed of angular fragments, of any composition, and above sand in size, when they are cemented into a solid mass, by any sort of cementing agent. Here the term is used in its broad sense, as compared with the way it was used under igneous rocks.

Breccias may result from the cementing of talus, but more often the breaking up of the material into angular fragments was due to other causes, such as crushing along a fault plane, or in the movements involved in mountain making. In such cases the breccia is of limited extent, but may occur repeatedly in the same neighborhood. Limestone, which has been crushed and then recemented, often makes a rock which takes a good polish and is used in several localities as an ornamental stone in place of marble, in fact often goes in trade circles under the name of “marble.” The breccia figured on [Plate 58] is such a limestone.

[Soil]

Over most of the earth’s surface there is a covering of rock waste, the product of weathering, some of which is unassorted, and some of it sorted by water or wind. This is all termed soil. It is an ever-moving cover resulting from the decomposition of the underlying rocks, to which have been added in places layers of rock waste brought from afar by the streams. Some soils are rock waste which had been carried clear to the ocean and deposited on the floor of the sea, and is now above sea level, because the floor of the sea has been elevated. Inasmuch as the underlying rocks vary in composition, and as there are areas of transported material, it is clear that the composition of soils must vary from place to place, both as to composition and texture.

Soils range from the finest, composed mostly of clay, to coarse ones, composed of sand, gravel or even boulders. Clay, the finest grained soil, is composed of particles only about ¹/₁₀₀₀th of a millimeter in diameter, of which it would take 720,000 billion particles to make a gram’s weight. Ordinary soils however have about 2 to 5 million particles to the gram.