vi PREFACE 



has to predict what they will be like by means of interpreting what he 

 has seen at some other place. He is well aware of the variability of 

 sediments, and on the basis of his past experience and his knowledge 

 of the mode of origin of sediments he is the person best qualified to 

 make predictions. A knowledge of the basic principles of sedimenta- 

 tion and stratigraphy is essential for this purpose. The geologist, how- 

 ever, also must understand the things the engineer wishes to do with 

 the sediment; and the engineer should understand the general geologic 

 problems involved and the limitations of geologic work, so that he 

 can utilize the services of the geologist intelligently. The engineer 

 above all should be conscious of the variability of sediments. It is 

 hoped that this symposium will help accomplish these purposes. 



Three types of earth materials are considered in this symposium: 

 (1) recent or slightly consolidated sediments; (2) ancient or maturely 

 consolidated sediments, that is, sedimentary rocks formed in the ge- 

 ologic past; and (3) residual soils, or soils weathered in place. Soil 

 technically perhaps is not a sediment, but as it has many of the char- 

 acteristics of soft sediments, particularly with respect to its effect upon 

 engineering problems, it is considered here. 



A sediment is an aggregate of solid particles that have been moved 

 from one or more places of origin to some place of rest. Its properties 

 depend on (1) the chemical, physical, and biologic nature of the solid 

 constituents, (2) the character of the material that fills the pore 

 spaces, and (3) the changes that take place in the sediment with time, 

 due either to applied stress or to chemical reactions. The practical 

 applications of sedimentation therefore involve both the nature of the 

 sediment and the processes that affect them. 



The symposium contains thirty-five articles grouped under seven 

 topics: (1) basic principles of sedimentation, (2) engineering problems 

 involving strength of sediments, (3) applications of processes of sedi- 

 mentation, (4) applications involving nature of constituents, (5) eco- 

 nomic mineral deposits, (6) petroleum geology problems, and (7) 

 military applications. 



The first topic on principles is essential for the proper understanding 

 of the economic applications of sedimentation. The second and third 

 topics, relating respectively to strength of sediments and the processes 

 of sedimentation, are of special interest to engineers. The engineer 

 must have adequate foundations for his structures. Frequently he is 

 called upon to build roads, airports, dams, tunnels, or buildings in 

 areas of relatively soft rocks, where he has little choice as to location. 

 He therefore must do the best he can with what foundation material 



