Particles that are more than 2 millimeters in diameter are not included in chemical, mineralogical, and some physical analyses, and they are called coarse fragments. Figure 20 shows the weight percentages of fragments in the total soil material at different depths. Soils that have a high percentage of fragments are less desirable for most uses. A high proportion of fragments, such as more than 60 percent in Laidig soils below a depth of 100 centimeters, dilute the effectiveness of the fine earth part of the soil (particles less than 2 millimeters in diameter). For example, if a horizon is 50 percent fragments and the fine earth is 20 percent clay, then the clay percentage for the total soil horizon is 10 percent. Analogous calculations can be made for other physical and all chemical properties of the fine earth.

Surface fragments dissipate some of the energy of raindrops. Therefore, soils with a moderate amount of coarse fragments on the surface tend to resist erosion. Percolation of water through soil is often more rapid where the percentage of coarse fragments is greatest, if other properties are similar.

The few fragments in Hagerstown soils are chert and are generally less than 2 inches in diameter. Morrison soils often contain much more sandstone than indicated by the curve in figure 19. Shale increases as depth increases in Leck Kill soils to the point where it is difficult to determine the difference between parent material and bedrock. The colluvial nature of Laidig soil is evident from the high content of shale and sandstone fragments most of which are more than 2 inches in diameter.

10/15/98