What is NOT a characteristic of masses found in soils?

The correct answer indicates that "always firm and rigid" is not a characteristic of masses found in soils. Soil masses can exhibit a range of physical properties, and rigidity is not a defining feature. In fact, soil masses can vary greatly in their texture, porosity, and moisture content, which can lead them to be soft, pliable, or even loose rather than consistently firm and rigid.

For example, the presence of clay can make soil masses soft and plastic, while sandy soils often have a more granular structure that can feel loose and less rigid. These variations contribute to the diverse characteristics of soil masses, such as their ability to compact, drain water, or retain nutrients, making the idea of them always being firm and rigid inaccurate.