PREFACE vii 



he has, and he is vitally concerned about the strength of the sediments 

 or their ability to support the designed load. 



The processes of sedimentation, especially processes relating to the 

 transport of constituent particles of sediments, have tremendous im- 

 pact upon our national economy. Millions of dollars each year are 

 lost by floods, beach erosion, shoaling of harbors, silting of reservoirs 

 and canals, soil erosion, and landslides. Engineers and geologists are 

 constantly called upon to cope with these problems. 



The nature of the sediments, discussed in Part 4, also interests the 

 engineer. This topic includes chapters on aggregate for concrete, sand 

 for foundry molds, and clay minerals. The last topic is of particular 

 concern to the geologist as well as to the engineer, because of the 

 materially different properties of the various clay minerals and the 

 different effects of base exchange upon clay. 



However, the economic utilization of the constituent materials of 

 sediments lies mainly outside the field of engineering. Both the min- 

 ing and petroleum industries depend on the products of sedimentation 

 for their livelihood. As McKelvey shows in this symposium, the total 

 value of economic mineral materials, exclusive of coal and oil, obtained 

 annually from sediments in the United States is almost one billion 

 dollars. A great many kinds of raw mineral materials are used com- 

 mercially, but space permits the discussion of only a few token ex- 

 amples in this symposium. These chapters, presented in Part 5, should 

 indicate to mining geologists the usefulness of knowledge of sedimen- 

 tation in their work. 



More than 6,000 geologists are directly or indirectly engaged in the 

 search for petroleum, which is found almost exclusively in sedimentary 

 rocks. In their training and in their professional work, geologists thus 

 become familiar with the applications of sedimentation to petroleum 

 geology. Rather than duplicate material of more or less common 

 knowledge to geologists, the Committee feels that it is preferable to 

 emphasize the less well-known applications of sedimentation and to 

 restrict chapters on petroleum geology (in Part 6) to a few topics of 

 current interest. 



Geology is of material assistance to the Army and the Navy during 

 time of war. Many of the geologic problems deal with sedimentation. 

 Two chapters on this subject are presented in Part 7. The usefulness 

 of sedimentation, however, is greater than these chapters indicate, as 

 work of a confidential nature is not included. 



San Francisco, California Parker D. Trask 



February, 1950 



