Ch. 1] IMPACT OF SEDIMENTS ON PRACTICAL ENDEAVOR 35 



materially affects the strength of the sediments. As Black shows in 

 Chapter 14, this question is essentially one of dynamic relationship 

 between water and ice within a sediment. 



The permeability and porosity of sediments are of great practical 

 importance to petroleum and mining geologists, to ground-water hy- 

 drologists, and also to construction engineers, because the movement 

 of oil and water through ground depends so much upon the permeabil- 

 ity (Meinzer, 1923; Muskat, 1937; Tolman, 1937; also Chapters 4, 6, 

 and 32 in this symposium). Once again it should be mentioned that 

 permeability is influenced by the size and degree of sorting of the con- 

 stituent particles; porosity depends upon the size and shape of par- 

 ticles and upon the load or degree of compaction (consolidation) of the 

 sediments. For example, it is well known that the water content of a 

 clay may be higher than that of a silt or sand but the permeability 

 may be less. Clays normally do not have a low porosity unless they 

 have been compacted for a long time. Permeability is of material 

 significance to the mining geologist because the ease with which min- 

 eralizing solutions and gases can penetrate rocks, particularly sedi- 

 mentary rocks, in many places is a major factor in determining whether 

 commercial ore deposits will be precipitated in the sediments. (See 

 Chapter 29.) 



Both the physical and chemical properties of the constituent min- 

 erals concern mining geologists in search of ore minerals. The manu- 

 facturer also is interested in the nature of the sediments as sources of 

 raw materials, as McKelvey points out in Chapter 27. The type of 

 mineral, that is, the relationship of molecules within the unit cell, is 

 of special concern to the manufacturer of clay products, as well as 

 to the geologist and engineer working upon construction, because of 

 the variation in properties with respect to type of clay mineral. At 

 times the geologist uses mineral composition as a means of tracing 

 sedimentary strata from one drill hole to another (correlation prob- 

 lems), or as an index of the environmental conditions of deposition 

 of the sediments. Physical properties of sediments are of special 

 interest to manufacturers of abrasives, insulation materials, or aggre- 

 gates for concrete. 



The mass properties of sediments, such as density, resistivity, radio- 

 activity, or compressibility, concern the geophysicist and geologist in 

 prospecting for oil, as indicated by Beers in Chapter 4. 



The processes that affect sediments concern all people who use sedi- 

 ments. The character of sediments and their response to stress depend 

 on the processes that lead to the formation of the sediments. In addi- 

 tion, the processes themselves have certain very special applications, 



