Geology of Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 42

most critical knowledge, however, gained from these procedures is the understanding
of how contaminants behave and migrate in these geological environments. We cover
this topic beginning with Chapter 7.

2.4.1 Identification and Classification Methods

The successful identification and classification of sedimentary deposits requires an evalu-
ation of several features, including the degree of sorting, grain shape, grain size, composi-
tion, thickness, and other characteristics.

2.4.1.1 Sorting

Sorting is the spatial arrangement of particles during their transport and deposition by
size. Sedimentary deposits range from very well sorted to very poorly sorted. The degree
of sorting in a sedimentary deposit or layer is controlled by the method of transport and
deposition. Sedimentary layers formed from wind transport are generally considered well
sorted because the wind can only transport fine-grained materials. Sedimentary deposits
formed from the action of glaciers are generally poorly sorted because glaciers are not
selective—they move everything.
Figure 2.19 shows gradational examples of individual grains ranging from well rounded
to angular. Figure 2.20 shows an example of a poorly sorted material.

Sub-rounded
to sub-angular Well rounded Rounded Angular

FIGURE 2.19
Examples of well-sorted, well-rounded, and angular sedimentary materials.

FIGURE 2.20
Example of a poorly sorted sedimentary material.