Page 108 - Moving the Earth_ The Workbook of Excavation
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ROCK, SOIL, AND MUD
3.2 THE WORK
FIGURE 3.1 Testing sieves. (Courtesy of W. S. Tyler Co.)
has no definite particle size. Organic materials may also consist of lime from shells or from lime-
stone originally formed from shells, and animal bones and excrements.
Rock. Geologically, rocks are classified as to the way in which they were made. Those which
solidified out of a molten state are called igneous, and are subdivided into volcanics cooled at the
surface, and plutonic hardened deep underground.
Sedimentary rocks are built up of soil or plant or animal remains and have been hardened by
pressure, time, and depositing of natural cements.
Metamorphic rocks were originally igneous or sedimentary, but have been altered by extreme
heat and pressure.
Figure 3.3 contains tables classifying rocks as to type and hardness. The latter quality is quite
variable, even in one formation, and may be made up of different factors, as resistance to pene-
tration, abrasion, or crushing.
